Unless somone else comes up with something, I got a catalogue through the post yesterday, with just the thing in it, but I won't be home til later, if no-one else come up with something, i'll let you have the name and web address this evening.
I just used ordinary wall paint (as I had a bin stolen before, and had no time to go out looking), but since then I noticed, a lot of hardware stores have numbers, that stick on permanently.
If you want to be really arty! plasicote paints go onto plastics. Availible at many DIY stores lots of colours and comes in pot and spray form. There are also lots of other makes usually in the decorative effects aisle!
To paint on plastic make sure the surface is really clean and grease free! You can also use ordinary acrylics but may need to key the area a little first (lightly sand). When dry if you coat with an acrylic varnish it will last longer. Even a coat of external PVA will help to preserve your work of art!