Disposable Plastic Lock (*NOT MINE*)

Description from Thingiverse. Original creator link: ChTuna 

These are simple one-time use disposable (Tamper) locks. They are designed to show damage if they have been removed.

Version 1 is less visible for tampering as the end is sealed inside.
Version 1 also has a smooth box for a note/ID to ensure the lock has not been replaced.

Version 2 is more "secure" as you can see the tabs through the bottom any tampering will be evident where with version 1 if the tabs are broken and reinserted, they are not visible.

You can also apply a little glue in the slot to ensure a higher level of tamper resistance.

These are not intended to secure anything but to show evidence of tampering or opening.

Here is an accompanying key holder for those who may be interested: https://www.thingiverse.com/thing:4607625