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.
Renewing a Driver's License at a Branch Office. A driver's license is usually valid for four years and expires on your birthday in the year shown on the license's upper-right corner. If you are under age 21, your driver's license will expire on your 21st birthday. Present your driver's license or acceptable proof of identity listed on the Applying for a License or ID form (standard license) or the Applying for an Enhanced License or ID form (enhanced license) when renewing at a Secretary of State office.