Were you parked in front of a business that has ever done valet? Valet isn’t typically something that just pops up as a one time thing. I think if you can prove historically that there’s no permanent signage and the place consistently does not have valet signs you might stand a chance. If it’s a significant enough fine (guessing likely if there was a fee associated with the tow) that it’s worth the day you’ll likely have to take, I’d fight it.