Mail Bag Labels

I collect a few mail bag labels which enhance my collecting area. I have seen hundreds of different labels from different countries. They all seem to have the same two cut-outs of the corners on one side. I was wondering if anyone could tell me if this is universal. Does this serve a purpose? Where do you think the idea originated? Any help would be greatly appreciated.

Can you scan an example of what you are referring to?

Would this be sort of like a parcel tag?

Thanks for your quick response. I am having trouble with uploading images. Mail bag labels are about 4-5" long rectangles. Most of them have the corners cut off with about a one-half inch cut on either the right or the left. Some have postal destinations dates etc. printed or filled in by hand on one side and the other side is usually blank. They usually have a punched hole for a string or twine which is then attached to the mail bag. I hope this is helpful. Thanks again. -r

You mean like these? (Googled and found this pic on the internet)
http://www.grosvenorauctions.com/dy.../65/7280.jpg