Do you live in an area where there are any deer?
Some of my neighbors do this they are pretty ugly but it works!
Get a deer shaped lawn ornament, the more realistic the better. Put it as close to the edge of the street as possible. Drivers will see it out of the corner of their eye and slow down to avoid hitting the deer.
They also sell those cardboard cut out things in the shape of a kid playing, you can always bring one out whenever your kids will be outside.
I also like the idea of putting up personalized signs, but keep the message as short as possible, you don't want to have distracted drivers instead of speeders!! The ones that the DOT uses at construction sites always get me "Slow Down My Daddy Works Here" written in that crayon looking font.
Or then again you could just get a sign that says "Slow down, speeding tickets will get you tasered"