Chen Lee aka SMGLee posted this photo on his Instagram account. It is a Glock Crossbolt Safety on a Taiwanese Police issue Glock 19. I have never seen this before, have you? Sure we saw the safety on the MHS Glock submission but that was a different design than this. The MHS Glock has an ambidextrous frame mounted safety that you flip up and down with your firing hand thumb. However this crossbolt safety is like your hunting rifle or shotgun where you push the safety from one side to activate it. According to Chen, this model of Gen 3 Glock 19 with a crossbolt safety is a factory feature from Glock and is issued to Taiwan and Portuguese police.
Here is a another photo he posted that I photoshoped to highlight the crossbolt safety. As you can see below, the crossbolt physically blocks the trigger from traveling backwards.
I wonder why Glock does not offer these or even the MHS 19 to the public? Sure we got the G19X but it does not have the frame mounted safety. Would you buy a Glock with an additional manual safety?