A long, long time ago I made these in 20mm, then destroyed all by accident when the lids depressed down into the box. Considering the time spent with decalsheets, plasticcard and braswire I was a bit gutted. A couple of weeks ago I found myself going over some of the colour prints I have with lots of signs on them and wanted to give it a go, but cheaper and quicker.
20mm round MDF base, drill a hole, glue in a toothpick. Snip off the pointy bit and smooth the underside of the base. Use a scalpel to slant the edges, add glue and sprinkle sand. Let dry, preferably not for 3 weeks like I did :P Snip the top to the required length and use a scalpel to get a nice flat surface where you want the sign. Cut out signs ( I use colour laserprints as those don't run and are very durable on regular print paper), add supeglue to the post and stick on the sign. Use a pointy toothpick to smear the excess superglue all over the back of the sign, this hardens the paper to make it really durable.
Then paint and weather to your desired needs.
Inexpensive to make and quick to replace if they have accidents.