I work at Lowes in the Home Decor/Paint dept. Yes you can paint concrete if you use a high quality exterior paint. People use exterior paint to paint concrete or cement block foundations. You do not put any sealer on top of the paint. The paint is a sealer in its own. You can use concrete stain that soaks into the concrete to color it but will look different than if painted. You can still see the "concrete" instead of "paint". After it is completely dry you can seal it with concrete sealer either to look natural or glossy. When you notice water soaking into the concrete after 2-3 years depending on the brand you use you need to reseal it. You can get the stain in 10-12 colors. There is a chart to choose from. I just did a concrete patio using the Quickcrete stepping stone form and then stained it brown after it cured. I got 17 stepping stones out of 12 80# bags of concrete. I only have about 50 more bags to go.
If you want to make a plaque with info as to where it came from you can use a wood plaque from Hobby Lobby, then stain it and write your message on it with paint or marker then seal it both front and back with Spar Urathane or Spar Varnish. The Spar is made to hold up outside. Be sure to put several coats on. It also has UV protection to help prevent fading. It won't stop the fading completely but helps. You could mount the sign underneath the seat to protect it further. Use a urethane adhisive caulk