MECHANIC: The American Sign Language (ASL) sign for "mechanic"
The "WRENCH"-based concepts of MECHANIC and/or PLUMBER are what could be considered "context-sensitive." If you combine the sign for "WRENCH" with [enough context] you end up meaning either "mechanic" or "plumber" -- even without adding the "person" ending.

Mechanic / plumber -- can signed either with our without the PERSON suffix. It depends on the amount of context in which you do the sign WRENCH.

The "low-context" version of MECHANIC / PLUMBER adds the PERSON suffix. If it is not clear that you are discussing a person (and not a wrench) then you can (and generally should) add the PERSON sign to the sign "wrench."

The "high-context" version can (and often does) drop the person ending because the meaning can be clear from the rest of your sentence. If it is obvious you need a mechanic and/or a plumber (and not a just a "wrench") then you can just sign WRENCH and don't need to add the person sign.

MECHANIC or PLUMBER:
This sign can also mean "plumber" if you are talking about water and pipes.