The first digit means something and sometimes the second number would mean a sub category. All other numbers were random. Most would use the number R11 or V11 if nothing is required. Something like R33 could mean a secondary search, V44 could mean an immigraton referal, R51 or V51 could mean documentation request, R61 could be a commercial shipment, etc.
Sometimes, we would use the code "LLPOF" (liar liar pants on fire) or some other ridiculous code to show we wanted a search...Usually on midnights or when it's slow to make the other officers laugh...but that wasn't usually cool with the supervisors in case that card ended up as evidence in a drug bust or something. Explaining that in court would not look good
There was also a code for checking out hot babes or German tourists without bras. Can't remember what it was...too long ago.