While it is permissible to remove the wooden stakes, it is a (minor) crime
to tamper with the iron pipe. Since utility companies rely on those
permanent marking devices themselves, they generally respect them.
Don't get caught removing the tag from your mattress, either. What happens
afterward is not pleasant!
The ones marking the front of my property were removed a few years back
when one of the utility companies came in and replaced the poles. The
stakes were pulled out with the old poles when they were removed.