Very cool idea!
More novelties brainstorming...
Engine - an homage to Mercedes history as an engine supplier.
Classic Car - One of the old models like the W196 chassis.
Brawn Add-on Kit - One of the coolest liveries in recent memory. Might not fit with the alphas, but a nod to Brawn would be really cool. If not, maybe just a reference to Ross Brawn himself.
"Turbo" key - maybe for the Enter key. Image or text. Merc have dominated the V6 Turbo era.
A silver arrow - Self explanatory. For the enter key or even on the arrow keys themselves if possible. Again, an add-on kit maybe.
Nurburgring/Hockenheimring Track outline - German GP locations. I was thinking of something Stuttgart themed, but I couldn't come up with anything that didn't make it look like Porsche.
Checkered flag - stolen from dilbertprogrammer's "torro rosso" set
+1 for "IN" and "Stay out" modifiers. Maybe add "Push" or "DRS"