Grammatically yes, you are correct. The term butler is only a noun, not a verb. Buttle is the verb that describes the act of someone who works or serves as a butler. You get a gold star, somewhere in your background you have a grammar teacher that is very happy that you were paying attention. ^_^
But stylistically we think “BUTLER ON!” is more fun. MMM, or perhaps Keep Calm and Sebastian On. That could work.
*ponders the mysteries of that, and the universe*
Words to live by.
Wouldn’t it be “buttle” on? ;)