can someone tell me how to make a sig
Go to the Image Manipulation forum
Find the thread that says "Request Sigs Here"
Ask somebody to make you one.
As for how to put it in the bottom of your posts, read the FAQ at the top of the page about how to post pictures.
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Get a copy of an image editing program, ie PhotoSuite, PhotoShop, or something similar. Play around with it. Make sure you keep it under 500 x 200 pixels, and ideally under 80K in size (when you open a new project in the program, it should usually ask you what size you want it, so you can enter the 500x200 there. Then, after you have it done, upload it to a website for hosting, like cardomain. Click on Control Panel in the top right, and go to Edit my Forum Options. There is a space for putting a sig there. Then you use the format [IMG]
http://www.whereveryourpictureishosted.com [/IMG] to call to it.
Or, go to Image Manipulation, and there is a thread where you can request that someone make you a sig. It's free, but it does take time to get to them, since there are a lot of requests, so don't be impatient for the favor. You'll want to post ONCE, with some pictures of your car if you want any inplemented in the sig, as well as anything else you would like it to have, say, etc.