Siggies can be about 600px wide and 150px high, but if you use a line of text (like you are doing) only 134px high. It can also only be 30kb in size.
If you are not sure how to check for size, just right click on the pic and click properties and it will tell you
Looks good but you need to compress the file size a little, yours is 44kb and you are allowed 30kb
Photoshop/PSP you go to 'save for web' and you can choose the file size or irfranview and xat.com both have good freeware image compression programs