If you just want to create signatures, not apply them to the messages as you send them to the messages at the server level, those web sites might be ok (but they aren't free and the first has nothing to do with signatures) but if you want to create a corporate-wide signature that is automatically added to all messages, you need a signature service that interfaces with the Exchange server so the signature is applied to all users - that is the advantage of codetwo, exclaimer and the others I listed.