Dish soap, Rubbing alcohol, a hose, a stencil and a can of spray paint. With the garden hose rinse the area down and wash with dish soap. Let dry. Spritz the area with rubbing alcohol. Let dry. Tape your stencils in place. Spray away lightly. Let dry in between coats. If you wish you can use a spray sealer once the paint has dried. I typically wash one day and spray the next morning. Just be sure not to spray on a breezy day so you don't end up wearing more paint than the numbers.
Stencils and spray paint...I used a primer first because cement is so porous. I also topped it off with glow in the dark paint. Daytime it's a blue and nights it's green. It actually has lasted about 4 years and no touch up yet.
You can make yourself a stencil by printing out the size and the font you want from a computer. You can print it onto card stock. Cut out the numbers with an exacto knife and then tape the stencil to the curb. Use a sponge made for stenciling or a stencil brush to fill in the numbers then pull off your stencil. It is quite easy.
After prepping the area as previously mentioned by others, we started with a rectangle of white paint, then black numbers, then topped with sealer. Shows up well and lasts for years.