Seth MacFarlane's House -- T.P.'d by Charlie Sheen Fanatics

"Family Guy" creator Seth MacFarlane's house was ruthlessly T.P.'d last night by a ragtag group of Charlie Sheen supporters -- and TMZ has obtained photos of the butt paper attack.

Sources tell TMZ, two unidentified boys and one girl snuck onto Seth's Beverly Hills property around 11pm and unleashed T.P. fury -- finishing with the coup de grace ... a sign on Seth's front door, reading, "WINNING! Tiger blood!"

It's unclear what provoked the vandalism -- but the poster also taunts ... "Roast this bitch," referencing Seth's recent Comedy Central roast of Charlie.

So far, no police report has been filed.