Homemade Airplane over Miami

These pictures were taken a few years ago in Miami, Florida. Someone was flying what appeared to be a homemade airplane over downtown. It must have been a wonderful view from up there, with massive skyscrapers and water all around.

Railroad Relic?

While biking on the Seminole Wekiva Trail and the Cross Seminole Trail through the Central Florida Area, I've been noticing several strange concrete markers with numbers on them. The marker pictured is located along the Seminole Wekiva Trail in Lake Mary. I find markers like this a bit intriguing, leaving me wondering what exactly they are marking. My guess is that they have something to do with the railroads that used to run along the sections of trail where the markers can be found.

Does anyone have any information about these, whether my railroad hunch is right, and what do the numbers mean?