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.
Your driver license is valid for 5 years and will expire on your birthday or 30 days after your birthday if you are turning 21. You may renew the license anytime up to 180 days before it expires (unless you are turning 21, in which case you must wait until your 21st birthday).