non= a negative, which by its position refers to the verb
vendo vendere vendidi venditum is a verb meaning sell, also sell out, betray, advertise, praise and recommend.
The "mus" is we. The "a" doesn't make sence to me, but Latin was a long time ago.
"We sell" should be vendemus
porci is either the singular Genative or the plural Nominative of the second declension masculine noun porcus meaning hog as opposed to sows or pigs in general. If it was the object of the verb it would be porcum (singular) or porcos (plural).
This must not be Classical Latin. It's probably medieval Latin which I did not study or it's a mispelling.
The closest I can come up with at the top of my head (assuming this is an attempt at Classical Latin) is "We hogs don't betray."
Is this the motto of a Harley gang? Although I'd prefer to see it start with porci rather than end, but it depends on the author, time and region. Languages change.
If Vendo switched from taking the accusative in Classical to the Genative in Medieval (and I don't know that it did) then it might be a corruption of the subjunctive and mean, "We must not sell of the hog," meaning "We are not allowed to sell pork products" which in classical Julian Latin I'd prefer to see ""non vendeamus partes suorum" although like I said, it's been a long time.