iboats has registration number stickers.
i used hardline stickers on my boat. i used the green w/ black outline...
just a thought. my nebraska boating rules book states that the numbers should be block letters/numbers. them green ones i got aren't block. very ledgeble, but not block. so far i've not been hassled by leo's about it. but food for thought depending on the rules in your state.
I know you said online, but I went to a local sign shop. I got exactly what I wanted, chose the color from way too many choices. They took less than a week and cost about $14.00.
I bought my stickers from the local hardware store. They need to be 3" letters/numbers and need to stand out easily. If the numbers go on a black color they should be white or a visible color, they also should be vinyl.
UncleWillie that site looks good...wish I had seen that before doing mine.
Being from Atlanta there has to be 50 sign shops close to you that will do this for a really good price installed so yuo won't even need to put them on and you can pick from thousands of different fonts