While I am on the trusting side when it comes to people, I do think it's important to have all your work marked with your personal signature. The 1st reason is so that you can receive the credit for your creativity & hard work, the 2nd is so that other people can't pass it off for their own. As much as I can't imagine why people would do that, it does happen.
I just had my own watermark signature designed by Melissa at Kulesa Design & I think she did a fantastic job. Melissa is very easy to communicate with & does a great job at interpreting what you want as an end result.
SO, if you'd like to check her out just follow my link & send her an email! She would love to hear from you.