Why do I have so many "A used LULU Signature ..." stuff inside my inventory? Is it safe for me to delete them?

The way the Signature Wear-on-Command and Re-rez system works is this:

each time you rez the toy (via chat command like "/1c" or via the HUD button), a new set is created in world, and is immediately put on you.
If you look inside your inventory, you will find that you are wearing "A used LULU Signature..." toy. That is by design.
if you detach that toy or set of toys whilst locked, a fresh toy or set of toys will be rezzed in world and put on you again.

So, your object inventory can quickly end up with quite a few "A used LULU Signature..." toys.

It is safe to delete them.

Tip:

Enter "A used" in the inventory search field to find all used toys. It's much easier to delete them this way.
Don't delete all of them - leave one or two. Here's why.