1986-P LMC Overcoat Crease Issue

DE, it comes with experience. But one bit of random advice is to think more in terms of what the devices should look like. Yes they can be smaller if the die has been overpolished, or larger if the die is old, but they will still just be what they should look like. When searching for doubled dies, it's not that one is looking for a second full bit on the devices (although amazing coins like the 1955 DDO have this and MD creates this but is totally different), in general you just look for the shape being larger in some way than it should be.

Sounds simple, but it's not. It's all about experience and we all found hundreds of MD, DDD, and similar non doubled dies before figuring out how to sort it all out. There are endless stories of folks who, after gaining experience, went back through coins they had already looked at and found great doubled dies.

My advice is always to look for what is outside of the normal design, not inside the normal. Can just be that wheat stems are too thick, or the FG initials on the reverse are too thick. Minor stuff, but still doubled dies.

As to the original coin here, to me, your coin appears to be a normal minor hit with the associated ridge. I'd toss it in a second. That said, maybe sometimes I toss important errors, but experience tells me that that fairly often I am right about a coin being an error or not even when I don't know exactly what is going on. So for questionable coins I post the coin here and usually get a determination. That's what you've done, and this has been a great thread. My opinion may be wrong, but overall most coins posted here get figured out with multiple eyes on them, and my thoughts are this is a random ding and the coin is just a cent.