Most Mexican states model their vehicle code after the state of Jalisco vehicle code. That state forbids an unlicensed motor vehicles on roadways under the jurisdictions of the municipios the counties.
In a nutshell ATVs are only legal on private land and they are definitely not legal on federal land like beaches.
The PFP and SSP are clear about catching undocumented vehicles on SCT highways. Federal highways. The vehicles are subject to immediate forfeiture, the driver to penal fines.
- "Beach" is a defined zone and it isn't merely sand located next to salt water. The protection of birds and turtles is a high motivator and tidal zones are different from hard packed sand bordering protected beaches
- Places infested with quads like San Felipe, have swarms of Quads but if they venture onto the intertidal zone the navy or the marines can sieze the vehicle
- Few tiny villages anywhere ban quads or unlicensed motor bikes. But venture outside of town and the policia municipal can raise legal issues
- Crossing a ramote road or using it for a short distance is often overlooked. Having a cop follow you for miles on a rural paved highway is another
- Most towns of 5-10,000 and larger outright ban quads and motorbikes in zonas centros (downtown)
- On SCE highways a PFP federal will overlook a quad or bike shortcutting across an undivided highway. Not so with divided highways. Farmers sometimes have shortcuts across Cuotas. The highway patrol often overlooks this
- The word regulated, in Mexico is an Oxymoron
- The only halfway certain way to know the local customs is to ask seasoned neighbors what is permitted and what isn't
- My son-in-law drives a quad on the beach. He is tasked with unearthing turtle eggs and taking them to the hatching shed. The quad is an artifact seized in Playa Azul some years ago and is the property of Pesca. Don't mess around on the beaches that is the one thing that flatly is not tolerated.