What are those arrow markings on the wing?
They are the overwing exit markings. You can see them in full in the following photo.



Boeing 737 Max overwing exits. By Oleg V. Belyakov - http://spotters.net.ua/file/?id=110706&amp;size=large, CC BY-SA 3.0, Linkec

This is because as already noted in another answer, B737 does not have self inflating slides for its overwing exits and as such, the passengers need some guidance for exiting, to prevent them from going the wrong way.



Pessini

The above image shows the procedure for using the overwing exit.