元 , traditional Chinese 圓 , is the generic Chinese character for "unit of currency" and is used to refer to the local currency: RMB in China, HKD in Hong Kong, SGD in Singapore, etc.
So odds are pretty high
the signs you saw were actually for prices in HKD.
While many Hong Kong shops do accept RMB, it's just a service for Chinese travelers and the exchange rate will not be in the buyer's favor.
You will not have much luck using RMB for buying a bowl of noodles.
However, there's an easy solution:
visit any of the foreign exchange shops found on every corner, many of which offer excellent rates for RMB to HKD.
Irrelevant but fun fact:
the Japanese yen and the Korean won are also cognates of the character "yuan", although the Japanese simplified their character differently into 円.
travel.stackexchange.com/users/1893/lambshaanxy
Most retailers in Hong Kong do not accept RMB.
The 7-11 stores* have an enlightend policy where they will accept RMB at HKD face value and give you any change in HKD.
As HKD are worth less than RMB they make a profit of the exchange rate on the transaction.
The current exchange rate is 1 RMB = 1.25114 HKD (April 2013), so the 7-11 stores are making an additional 25% profit for their kindness.
Some other sellers MAY accept them but my recollection is that most will not.
Trying to use HKD in China is about impossible.
Note that in most of Asia NO commission or flat fee is payable.
The rate offered applies $ for $ or whatever.
In eg Australia they charge an iniquitous up front fee and changing enough to get eg $20 for a cofee may give you only $A5 or less.
Utter thievery.
While, as uncovery says, there are a very large number of money changers in HK, I have found that banks and specialist big-business money changers offer poor rates and that the best rates of all are offered by a small number of small businesses if you know where to look.
I stay in Mong Kok when I am in HK (noisy, busy, cheap accommodation, more "authentic" than many areas, fun) and have found a money changer who invariably offers superb rates - about 0.5% off the actual exchange rate either way.
Stunning.
Location below.
As I wander the city I note the various rate offered and in quite a few visits no other money changer has bested these ones.
Taking subway to Yau Ma Tei (quick cheap ride from city centre) and exit at A1 and walk West along Pitt Street and you may be at their door - or, see below.
Rate assessment:
You can instantly determine how good a rate a money changer is offering by asking their cash buy and sell rates between two currencies ( or buy rate each way or sell rate each way, which gives the same result.)
The mean "markup is ~=
($buy-$sell) / ($buy + $sell)
Close enough
you can use buy-sell difference / $buy/2 ( = same as buy-sell difference / (2 x $buy))
eg if some one is trading HKD-RMB, if they offer 1.2 HKD per RMB if buying RMB (or selling HKD) and 1.3 HKD/RMB if selling RMB (or buying HKD)
Then markup = (1.3-1.2) /
(1.3+1.2) = 0.1/2.5 = 4% The simpler method gives (1.3-1.2)/1.2 / 2
=
0.1/2.4 ~=
4% close enough.
Purists will argue that the true rate is square_root($buy x $sell) but, again, the result is not much different.
For any given currency pair just look at the buy-sell difference.
The smaller the better.
ForEx who seem to have booths in all airports and elsewhere offer consistently very terrible rates in my experience.
Western Union are not usually very marvellous.
Hong Kong's cheapest rates: Location:
Please excuse degree of uncertainty.
I will have photos but probably not findable in your time frame.
Location is "probably" where two red lines are.
I start from Mong Kok proper near subway just above top of picture.
Walk down Nathan road and after a few blocks drill in sideways.
You can spot them by the queue !!! :-).
Two cashiers AFAIR opening onto street.
Two small fast moving queues of happy customers changing all sorts.
About 2 or 3 doors along further off Nathan Road on the same side is a Western Union office with 3 cashiers and NO customers !!!!!! :-).
Fast, polite, professional / business like.
No Chinese language needed.
"7-11" stores are unknown in my country (NZ) but are much the same as 7-11 stores in the US - corner stores selling food, groceries, drinks etc. ).
travel.stackexchange.com/users/3301/Russell McMahon
Looking around online ( ask.com , Yahoo Answers ), the conclusion seems to be that you can spend RMB only in certain bigger shops that advertise this with the Yuán sticker on their window or the cash register.
For other smaller shops, street vendors or taxis
you can not use RMB.
As usual the exchange rate you get is not as good as through a bank, currency exchange or ATM.
My advice would be to always use the local currency.
travel.stackexchange.com/users/1317/Peter Hahndorf
No you cannot reliably use Renminbi/Yuan in Hong Kong, you will have to exchange it.
Taxis generally do not accept them.
Other shops generally do not display if they accept RMB or not, and if they accept it, you will most likely get change back in HKD.
You can either exchange at a bank or at one of the hundreds of money changers in Hong Kong.
To my knowledge, HSBC is giving the best rates.
travel.stackexchange.com/users/3778/uncovery
The supermarket chains in Hong Kong (such as Welcome) do accept RMB at a (not great) fixed rate.
There are otherwise no fixed rules about which businesses accept RMB, however it is better to assume that most businesses do not.
That said, Hong Kong is changing fast with the increasing amount of mainland tourists.
RMB usage is definitely rising throughout the city.
travel.stackexchange.com/users/None/
While travelling in Hong Kong, I noticed signs at several vendors advertising prices with the 元 character, which from my visit to Shanghai I recognized as the symbol for Yuán.  Since Hong Kong has its own currency, this confused me.  Do vendors accept Renminbi in Hong Kong?  Does it vary depending on where you go, or is acceptance (or non-acceptance) universal?  Does an exchange rate apply, or are HKD and RMB considered interchangeable in Hong Kong?
Can I spend Renminbi in Hong Kong?
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<money><hong-kong>
travel.stackexchange.com/questions/4573
travel.stackexchange.com/users/None/
Larger shops are increasingly likely to accept RMB, but probably at a disadvantageous exchange rate and with change in HKD. Most retailers, especially smaller shops and restaurants, will only accept HKD. It is considered possible to use RMB in bigger shops and supermarket chains in Hong Kong. However, for smaller purchases, it is necessary to echange them for local currency.
RMB are accepted at some shops in Hong Kong, mainly bigger supermarkets chains, 7-11 stores. However, RMB use seems to be increasing. Small purchases cannot generally be made using RMB. It is better to exchange them for local currency. Shops may accept them but give change in local currency.