When I was adding my distance markers, there were some places where there was no catenary mast or tunnel on which to affix the signs. They thus had to have their own mounting pole.
I decided to glue them onto a pin that had had its head cut off. This works OK for a sign on one side, but if there has to be back-to-back signs, they tend to stick together and not stay parallel. I therefore decided to use two pins per sign. This shows how I went about doing that.
I first dip the back of one sign in a blob of wood glue and lay the sign face down. Onto that I lay two decapitated pins. (When cutting the heads off pins, hold them in a trash can and close you eyes, the heads shoot off like bullets and can seldom be found.)
I then pick up the sign by the pins with tweezers and hold the sign in place while I tap the pins in with a small hammer. It is tricky and perhaps waiting for the glue to dry before installing them would make the job easier.
Here is the result. On the left is a single pole sign and on the right the better double pole version.