This how-to will walk you through the creation of a digital signature file. Useful for signing documents on the fly and emailing them back and forth, which saves on postage and lessens paper usage.
Step 1: Make Your Mark
You need to start with your signature on a sheet of paper. In the hopes of not being blatantly thiefed of my identity, I have elected to use John Adams as an example.
Step 2: Scan the Sig
You need some way to get this signature into the computer, an optical scanner is probably your best bet, but in dire circumstances, you could use a digital camera.
Step 3: Import the Scan to Somewhere Useful
I prefer to use MS Paint on a Windows machine, but its up to you. On a Mac, I've always scanned in Photoshop, but again, your choice.
For a more free flavor, once you have the scanned image, all the following steps can be done in Graphic Converter, a free program for OS X (and legacy systems, too).
Step 4: Save It in a Useful Format
Once your signature file is in the correct orientation, save it.
I find that the .PNG format is the most useful for signature files, but I am by no means an expert.
Step 5: Insert It Into the Document
You need a document that requires your signature, I suppose.
I most commonly am using Word, but there are plenty of other programs that can insert images.
Step 6: Protect Yourself
I suggest outputting only in a PDF format due to your signature being quite easily "re-appropriated" otherwise.
On OS X, just choose print and int he PDF pulldown menu, choose save as PDF.
On XP or similar, you'll need a PDF creation tool (try googling "XP PDF Creator" for some free ones, like that pictured). Rumor has it some versions of Word come with this as well.