If the stereotypical tattoo for deck hands etc is to get a fouled anchor to symbolize the trials and tribulations of sea life, and on uniforms navigation gets anchors whilst engine gets propellers, wouldn't a good tattoo for engineering be a fouled propeller? I was thinking propeller with a leaking stern tube, but how do you draw that

A prop with a physchadelic rainbow effect?

Some combination of a gear wheel, a prop, and a timing diagram.

Or bulbous bow symbol on your hip or something lol

"MSD Discharge" with an arrow pointing down for a tramp stamp. ["My" Sanation Device.]

I like the MSD thing, although I think tattoos are way overrated, unless of course you have earned them - whatever that seems to mean.

Agreed, it bugs me as a sailor when non-sailor hipsters get traditional sailor tattoos... The wimps wouldn't survive on a ship - lack of safe spaces and too many microaggressions going around lol