Got some new christmaslights that needed hanging outside. After looking at regular weather-resistant hooks and their pricing, I ended up designing my own and using regular outdoor woodscrews. 

This is what I ended up with, should work on both fascia and soffit and uses a single 4.0 panhead wood screw. (Which is much cheaper than a weather resistant hook where I am from at least).
 

2 versions: (Select download STL/CAD to find the 2 versions)
1 with a lip to keep it oriented against an edge
1 without the lip

Print Settings

Printer: Prusa MK4S
Support: No
Rafts: No
Noozle: 0.4
Resolution: 0.2
Infill: 15%
Perimeter: 3
Notes: 

Used concentric top/bottom layer infill
Printed in PETG for weather resistance and some flex in the clip/hook.

Additional hardware needed:
1x 4,0x20+ panhead screw (type depending on material)