The Signature toys are no-mod, so you cannot adjust them the normal way.

To adjust the size,

• click on the toy button on your HUD to open up the toy menu.
• on the blue menu, select "other...", then "re-size"
  • for Signature cuffs, you will be presented with another menu. Choose  "wrists", "ankles", "arms" or "thighs".
    (if you are wearing your arm or thigh cuffs and don't see the option, try rezzing another set. If that doesn't work, try re-activating that particular plugin - it means Second Life has borked thints again).
• now you adjust the size by speaking on chat channel.
  • if you want the the size bigger by 5%, say 1.05; by 10%, say 1.1 etc. This means it will grow bigger by 5%/10% from the original default size.
  • if you want the the size smaller by 5%, say 0.95; by 10% say 0.9 etc.
  • if you change your mind and want to reset to the original size, just say 1.
  • if you are wearing your Signature gag and are using the Restrained Life viewer, you will instead re-size on your command channel (default is "/1") instead of chat channel. For example, you need to say "/1 1.05" to resize it up 5%.