I can see limiting the number of garage sales, no one wants a weekly swap meet going on next door every weekend, but 3 per year seems low.
Signs are need, without signs people won’t know where or when they are.
We (and a few neighbors) had a garage sale a few weeks ago. and we put up signs in places that may have violated the ordinance. We also drove around after the garage sale and took down all our signs. I think there should be an ordinance saying if you put a sign you need to take it down after the fact.