This is something Google has failed me on so far, I am looking at replacing a part in the engine bay this afternoon and when I took a look at the fasteners holding the part onto it I noticed that somebody at some point in time has drawn blue lines through the top of the bolt heads.

Can't think of why anybody would do this, whether it was done at the factory or afterwards... anybody have any theories? It really doesn't matter for my job at hand but I'm just curious.

 

I means it has been torqued to specs and for future reference, to see if the fastener has loosen.

 

It'd done during assembly. If you take a look under the car, you'll notice a lot of strange markings.

 

Maybe I should have paid attention to it, I replaced the cold start injector and only after I had everything apart did i realize my clicking torque wrench no longer clicked so I just tightened everything as tight as it would go without putting gorilla force on it. I didn't think to try to make the markings match up to where they were before...

However I would have expected the markings to extend outside of the bolt head to the attachment point surrounding them if they were meant to denote proper position - oh well, the bolts didn't break and nothing cracked and fuel didn't leak out so I'm sure it's fine.