Lock-in props are often items used for peacocking, such as a cool cowboy hat or a scarf. Lock-in props are useful for creating comfort and can be combined with a takeaway to have the target chase after the PUA to return the item.
It is important to remember to have the target return the lock-in prop, as if solid-game is not run, the item could be lost, either from the target stealing it intentionally or, more often, from forgetting that she has it.
When a genuine connection is made with a woman, the PUA can sometimes gives her a lock-in prop until their next meeting, thereby anchoring his presence with her through his prop (i.e. a mood ring or bracelet).
Mystery on lock-in props at 0:45:
That scarf would make a great lock-in prop!