Weddingbee boards

I have a couple questions about shower thank you cards.  Even though some gifts were purchased off of our registry (so are for both of us), should the thank you notes be signed by just me? 

And I also received checks from a couple of people (my mom's friends) who said, "You're old enough now, you shop for yourself."   Does the same rule apply (i.e. note just from me)?  And I wasn't quite sure based on what they said, but did they intend for me to spend it on myself?  Or for our home together?  I don't know if that's a weird question, but several of the gifts I received were things like jewelry that are really just for me.  I just don't want to write something like, "Thanks, this will help contribute toward our house downpayment" (or whatever) when they were really hoping I'd use the money to buy myself a purse or something.