What is the logo gear worn by non-commuter cyclists? I live in the suburbs where there are many routes for road cyclists to go for rides.  I assume these cyclists are riding for fun and/or exercise and/or to train for some kind racing events.  Sometimes they are alone, other times they are in pairs or small groups.

Many cyclists have big logos on their shorts and shirts.  What are on the logos?  Where do they get them?  I don't see these in the online bike equipment stores.  I can only guess that these are associated with professional racing.  In any case, it seems that casual cycling folks don't have normal access to big-logo gear.  Where would I get some?

(I don't mean to sound judgemental, but I see it a lot but don't know where the gear comes from.  I am curious about biking communities and what they wear.  I am interested in hearing from those who wear such gear.)
There are different types of logos which get worn for different reasons. Bike clothing may include logos associated with:


Clothing manufacturers: An otherwise plain jersey will often include the logo of the manufacturer. This is common for athletic clothing in general.
Employers: Companies often make jerseys with their logos that (presumably satisfied) employees can wear to show spirit.
Sponsors of professional teams: Fans of professional cycling teams may choose to buy articles of clothing that are replicas of the official team uniforms. These items include the logos of the companies that sponsor the pro team.
Local clubs or teams: A local cycling club may have their own un-sponsored logos. Organizations can order custom kit in much the same way people order custom t-shirts or team bowling shirts.
Sponsors of local clubs or teams: A local cycling club may have team apparel that includes logos of the local bike shop and other local companies that sponsor the team. These items may be offered at reduced prices or even for free to club members.
Races or organized rides: Some races and supported rides give or sell participants commemorative jerseys, which may serve as a memento or badge of honor.
Advocacy groups or messages: Cyclists may wear clothing to show support for a message or for an advocacy or non-profit group. For example, jerseys may include designs featuring the "share the road" message.
Abstract design: Jerseys and shorts may feature designs that are designed to just look good. For example, one manufacturer sells jerseys featuring an imaginary team and based on professional kit from  50 years ago.