Memory or no memory?

I have a SE Crew cab that rolled on the side and the left side mirror (tow package) has to be replaced. Since I bought the vehicle used, how would I know the difference if the mirror should be with or without memory? There aren't any obvious buttons besides the mirror positioning button. I don't want to purchase the incorrect mirror as I was informed they are not interchangeable. I appreciate the help. Thanks.

if your buying it from a dealer then if you give them your vin # they will get you the correct mirror. your vin tells them what you have if your not sure.