I don't get asked questions often enough to have anything like a Frequently Asked Questions list. But one of the few that I have been asked more than once is "What do you do if a marker is missing when you go to collect it?"
This does happen from time to time. Markers become damaged when struck by a vehicle or a very large animal and need to be replaced, or they get removed for refurbishment and then put back later. On very rare occasions they can even be stolen, although how (or why) anyone would steal a marker is beyond my comprehension. Those things are pretty big and not exactly easy to carry around.
Usually the PHMC is aware of the situation, since they of course are the ones who repair or replace the markers in question. But if you ever notice that one is missing, you can make sure that they know about it. Just follow the steps outlined on this page to first confirm that they don't already know and then, if needed, to bring it to their attention. They'll appreciate the help!
But to answer the actual question, what do I do when a marker is missing? Apart from what I've just stated here, I take pictures of whatever is available in the area, if it's related to the marker subject. You know, all the things that I would normally photograph for a post anyway. Usually, I will then wait and hope that the marker returns soon. I absolutely will not take a picture from another source, unless the photographer gives me explicit permission. But I thought it would be funny to do something a little different, so we're going to visit a missing marker this week.