I always pick up the pace when I run past these signs. If there are no other cars around to disturb the speedometer it will say I'm doing 8mph on my easy runs. That sounds about right since I'm under 7:30 mile pace.
Sometimes I use it to my advantage to impress people nearby, especially colleagues or girls. There is a speedometer that is close to a 7 11 shop near me. Yesterday I saw a girl walking towards the shop. I was standing behind a bush with a full bottle of gatorade. I got onto the footpath and immediately sprinted as hard as possible. Just as I passed her the sing said 15mph and I made myself look as relaxed as possible passing her so she would think it is just an easy run and not a sprint. I took my gatorade and attempted to drink a big gulp. Some went down the front of my shirt but I didn't mind because she was behind me at that stage so it didn't matter if I made any mess. I came to a stop when I reached the shop, hoping that she would also stop to go in too. I stretched for a minute and let myself recover and get my breath back to normal so I could talk to her. She reached the shop after a minute.
I started talking by apologising if I accidentally brushed into her when I was jogging past. I told her that I was doing a marathon paced run and I just done 16 miles. I told her that I'm training for a hard marathon. She was impressed by my pace. I offered to buy her a take away coffee in the 7 11 and I walked with her a bit while we drank. She is from Estonia but has lived in Tulsa since middle school. We are going to meet up again soon in Starbucks. I can't wait. Thank you speedometer!