There are a few ways you can "sign" electronic documents safely and securely. One way is to scan a copy of your signature and insert it as a photo. Next you must password-protect the document or make into a PDF so that it can't be modified. It will basically look like a signed fax.

The other way to digitally sign on the dotted line is to use electronic signature software, such as a program by Silanis, which technically binds your signature or "mark" to the document and can indicate if your signature has been tampered with or not.