Since you're dealing with municipal corporations, it's COMMERCE, so you can ACCEPT the ticket CONDITIONALLY. Here's what I'd send them with the ticket back:
"Dear sirs, I conditionally accept your claim that I owe you some payment for this alleged violation, upon proof of claim that we have a contract. If you fail to present me with evidence that such contract exists within 14 days, I will consider it as an admission that no such contract exists and you may be estopped to claim otherwise at a later date.
Furthermore, I request that you identify the holder in due course or the real party in interest, who's rights are involved in this matter."

Now the ball is in their court, with a copy of the letter and proof of mailing being a proof of their commercial dishonor (failure to answer your C.A.), unless they provide you with evidence of their authority/contract.

Definition:
REAL PARTY IN INTEREST:
"A real party in interest is the person or entity whose rights are involved and stands to gain from a lawsuit or petition even though the plaintiff who filed suit is someone else, often called a "nominal" plaintiff."