There is another way, but it will get a little tricky.
Outside of the transaction IE03 you can check for the existence of attachments for a piece of equipment by looking in table SRGBTBREL. Field TYPEID_A will be "EQUI" and field INSTID_A will be the equipment number, zero-padded on the left to 18 characters long. Use SE16 to look in the table and you'll get the idea.
You could wrap this test in an RFC-enabled ABAP function and call that from your Personas script button. Use the return value from that RFC to decide if attachments exist or not and how the script should respond. Details for how to write such an RFC and call it from a Personas script are in this blog: Calling RFCs from a Personas script.
Like I said, this isn't straightforward and perhaps Personas scripting should include an active/inactive test in addition to the exists/doesn't exist test. Until then, however, there is a way if you don't mind a bit of ABAP programming.