How can I prevent theft of mirrors? I want to know to permanently fix back view mirrors. Last night, somebody stole them.
Please tell me any solution.
Make your bike less accessible.  Don't park it near where people walk past.  Instead, park it down the row a little.  Avoid parking it anywhere that will be in anyone's way&mdash;inconvenienced people may take it out on your bike.

Park your bike in a secure location if possible.  That means not leaving it outside overnight; ideally bring it into a lockable garage or shed, or even into your home.

Make the accessory securely attached.  That means no velcro, no quick releases, and no breakaway plastic.  A downside: breakaway parts are a safety feature to reduce the chance of stabbing into you or someone else.

Also, look at the fasteners.    If it's a thumbscrew like a GoPro, anyone can undo that without tools.  So look for replacement metal bolts that can be torqued down tighter.  Ideally the new metal bolts would be into metal fasteners&mdash;plastic ones may strip out easier.

To protect the bolt, you can use some weird security tool fitment that the thief won't be carrying on their person.   Or consider putting a blocker in, like a ball bearing into a hex socket.  You can retain it with candle wax or glue, annoying to remove legitimately.

Also prevent the bolt being removed by using a thread locker like locktite. Generic superglue/cyanoacrylate glue also works fairly well.  Avoid the threadlockers that need heat to release, else you can't get your own parts off without a hot torch which will melt other things.

An additional thought&mdash;depending on how your bike bars are set up, it may be reasonable to wrap your bartape over the accessory fitments.  This will obscure the fastener and make it take longer to interfere with your bike.  

Naturally these suggestions won't make your bike theft-proof, just make it less-attractive and take longer to fiddle with.