Bluetooth paired signal
According to the HC 05 AT-command set, you can verify if the module is paired (and the title of your question suggests, that this is what you need).
Please check the AT+STATE? command on page 16:

The command: AT+STATE?
Response: +STATE:[Param] 
where [Param] denotes the state:
"INITIALIZED", "READY", "PAIRABLE", "PAIRED", "INQUIRING", "CONNECTING", "CONNECTED", "DISCONNECTED", "NUKNOW" (unknonwn - isn't it a mistake? shouldn't it be "UNKNOWN"?)

Update

In the document HC Serial Bluetooth Products
User Instructional Manual, on page 32 you can find the following information (original spelling):


  PIN32 - Output terminal. Before paired, it output low level. Once the pair is finished, it output high level.