Ah...dear Red doesn't know about ironing blue boxes. I'll have to fix that.
Maybe Sylvia or someone will have the photo descriptions (or it's in the Playmobil Collector) but the idea is that it makes it so you can open the box with ripping it up. On many items I don't care much about the box (though I am careful) but for something very rare or special where you want to keep the box as pristine as possible.
Basically, you can iron the flap (on low, placing a cloth between the box and the iron...and it will warm the adhesive so you can open the box without damage. (Also, make sure not to use steam.
)
It's like magic!
Photo courtesy of www.Playmobil.de