Among other uses, I put a ziptie through each hub quick-release lever and then around the fork arm/chainstay (I have XTR QRs, which have a convenient openwork handle... put them around other types). It's my eyes-only tamper-indicator since I have to park outside in busy areas.

They're not anti-theft devices, but a quick glance tells me that the QR hasn't been opened or loosened.