Green’s Dictionary of Slang

C.A.N. n.

(US prison) Crime Against Nature, an illegal homosexual act and therefore the prisoner who has been convicted of it.

[US]J. Blake letter 7 Feb in Joint (1979) 199: He has been put in the tender care of the ever-lovin’ Doctor [...] in order to escape being deep-froze on a C.A.N. charge, which is Crime Against Nature, only whose they don’t say [Simes:DLSS].