13 cool tattoo probably the Mary Jane interpretation is right but a tattooed 31 literally means wank in Turkish street parlance 3 looks like a gripping hand and the 1 - well you know what that looks like. So the lyric means he is such a looser that he wanted to link himself to illicit drugs but ended up being branded a wanker. Thats how Ive always interpreted it anyway. Blessings...
The tattoo artist drew a transposition. 31 is a transposition of 13.
Fairly common mistake in bookkeeping/accounting. The difference is
always divisible by 9.