you probably wouldn't see the signature through all that dirt anyway, LOL ...
"Roush" is an aftermarket modifier of Mustangs (and other cars). They start with a normal Mustang and then add their "upgrade" package to it. There are several different Roush packages, and some of them do not touch the engine at all because they are appearance only packages. I am not sure if they put a signature or badge on all of their cars, but it might be on the dashboard, not on the engine.