I love this idea, as someone who would love to put "On Duty Mechanic - Call Elias @ 123-4576" on the wall of my mechanic shop, or even at any player owned businesses so they could advertise. Maybe make them only available for at the most 24 hours.
If people abuse them, just punish them for it, whenever you run the command to place one just create a log so they can be easily tracked. Sure there might be some people who abuse it but it would be the same as unrealistic building where it just gets reported and taken care of with a notice to remove it.
For a trial, we could try to allow admin markers for RP use ICly, use a /report 1 to get it approved and see how they work along in the server in an attempt to gauge how often or how much of a use it could have!
Implementation,
It can be removed the same way how blips can be removed by the owner with /removeOrderBlip to clear it if you are done with it.