The main signs of needing an alignment are the car wanting to pull to one side or the other, or strange tire wear. Just make sure the tires are inflated to the proper pressures and they aren't showing any external damage already. A shimmy or vibration is not usually related to alignment and indicates something spinning is out of wack or unbalanced. The car pulling to one side when you apply the brakes is usually brake component related.This is just a short basic list. A positive check is to get it checked on a good 4 wheel alignment machine. My dealer has a 1/4 million dollar machine that is dedicated to M-B autos primarily.