I came across this home made repair to a bicycle seat post. People put a screw in the seat post in order to limit a seat to slide down. It might serve another purpose too. In this bike’s case. The tube have been drilled a few times. My understanding of this is that the post was too narrow for the seat tube to hold. I can’t really see someone putting a screw in a seat post for no reasons.
The victim was a Super Cycle Chinook for kids. Note the 2 holes under the screw.