I also love historical markers. The way you've added the link to the marker is excellent. We get to look at the marker and see other information about the marker and it's subject, and no copyright laws have been broken.
As a caution to wikitreers in general: Photos that you did not take, belong to the person or agency that took them. They are copyrighted and as such should not be copied to Wikitree without permission. Sandi's example is perfect.
Link don't copy - This goes for Find a grave also.