I looked up acronyms for PU, the only one I could find relating to smell would be pig urine. But all of the other info about it I found said that it doesn't actually stand for specific words starting with the letters P and U. Here is the best answer I found from the website- The Phrase Finder:
National Transport Authority > Taxi and Bus Licensing > Taxi > SPSV Driver Licensing > Renew an SPSV Driver Licence. A regular SPSV driver licence is valid for five years and is renewable; a local area hackney driver licence is valid for three years and cannot be renewed. (The holder of a local area hackney driver licence who wishes to continue operating can, however, apply for a new licence.) To renew your SPSV driver licence, you must hold: 1  A valid full Irish driving licence or equivalent; 2  A valid SPSV driver licence; 3  Must be Tax Cleared with Revenue.
There were 13,605 taxicab medallion licenses in existence, 368 of them having been auctioned by the City of New York between November 2013 and February 2014. Each of these new medallions was earmarked for use with a wheelchair-accessible vehicle. Taxicab vehicles, each of which must have a medallion to operate, are driven an average of 180 miles per shift; the average total number of annual taxi passengers is 241 million.