You don't need to spend money on a program to make signatures. You can use a free program like "The Gimp" to make a signature banner.
Here is another free graphic program:
And yet another free one:http://park18.wakwak.com/~pixia/
If you want to buy a program, you might want to consider what your needs and budget are.
Photoshop is about $500.00 and up. In Canada it's about $700.00.
Paintshop Pro can do almost anything that Photoshop can do and it's about $120.00 or something. If you end up getting Paintshop Pro, I have a series of beginner tutorials at my website. If you get PSP and want to do the tutorials, just PM for the link.
But IMHO there is no need to spend money on a graphic program just to make signature banners. A free program will accomplish that and a whole lot more.