The S&W Model 10 M&P is a weapon in Mafia: The City of Lost Heaven. It's a .38-caliber, six-shot handgun initially developed in 1899. It has been used by military and law enforcement alike.
The weapon is commonly used by the police patrolling the streets. If you get a higher wanted level the police will start using shotguns and Thompsons.
You can find more real world information about the S&W Model 10 M&P on its Wikipedia page.