I shouldn't be talking as I had set aside both my model railroad and working on military miniatures for almost 30 years and just got back into both hobbies. And yes that means that I'm using a lot of thirty-year-old cans and bottles of paint. I tend to weather my kits so there is an underlying need to get the colours close to right but not exact because in real life they only were that way when they came out of the paint shop. After that they fade and are scoured by trees and bushes and stand at varying levels of dust and dirt and grime and hand-painted touch ups.
When it comes to tac signs its almost impossible to hand paint those. In real life they are always stencilled so they are pretty uniform and "crisp." I've found the only way to replicate that is with a good decal set - Microscale is a good line for that.