It always amazes me what people throw away & discard. Some can't see past worn & torn, battered & old, but lucky for me I can. I can see the potential were it doesn't exist. It makes me feel good to repurpose a piece & make it pretty again.
I found these on the side of the road & immediately knew a fresh coat of white paint & some fabric would do the trick. After painting them I decided to do something a little different with the seats. I bought a $5.00 drop cloth from the home improvement store & stenciled on my boys birthdays with a thick soft beach blue stripe down the middle. I created the stencils from my computer. I simply printed each number on thick card stock, adhered (with tack spray) it to contact paper, cut them out, torn off the backing & voila you have a "sticky" stencil that will not move or shift when you paint.
The entire project cost me under $15.00. Sometimes finding a sturdy piece with good lines either at a garage, tag sale or occasionally on the side of the road pays off. The end result is worth every bit of effort.
It is a good question. I am not sure how & why other people use numbers but I use numbers that have significance to my family, such as anniversaries and birthdays. These are my boys birthdays.
Have a nice day!