Remixed version of montereypcrepair's Ar15 Back Sight. I Remodeled the entire thing but the overall look is the same. I made it easier for 3d printing and set the file up for easy engraving (hence "Turk" in 123d file) and I use these on airsofts, not just m4s
Instructions (123d Design):
Remove "Turk" its just there as an example
Change the text or add in 2d vector (or another 3d object if you choose)
Extrude text and mirror
Place extruded text on both sides of the sight. Make sure they are overlapping!
Use the "Subtract" tool, click the sight first (as target) then click the extruded texts and press enter.
Export as 3d, STL (for 3dprinting) and to be safe check "Combine Objects"

Origonal: http://www.123dapp.com/123D_Design/Ar15-Back-Sight/4289187
Mine: http://www.123dapp.com/123D_Design/Turk-rear-site/5350599