Silver is a basic level. You get a 20 % point bonus and the opportunity to use the Ultimate Reservation Guarantee. For silver and gold members, this guarantee will give you $100 cash for getting bumped at limited service properties. At full service properties, you are entitled to $200 cash and 2 free night certificates (good at any Marriott property that has a room for sale).

Some properties may offer silver members a few extra things like a small gift. I never experienced this when I was a silver member, but it has been reported on FT.