As many above have said, if the first letter is the same, it doesn't matter much. So if legal name started with D, you're probably in the clear. If not, just learn how to write a D and then your signature can be D-squiggle-squiggle-squiggle.
That's how a lot of people sign things, anyway. Over the last 15 years my signature has devolved from extremely legible and on point to C-Ihavenoideawhattherestofthatsays. The older you get and the more things you have to sign, the less you care and wanna get the signing over with already.
Or, if you really would like to write your name perfectly, you could practice at home a lot. Try writing Dean over and over until it feels natural?