I'm sure most people know this or have figured this one out, if not hopefully this is of some help! (Frustrating for sure...)
After an install of SW 2016, diameter symbols were not showing during detailing!
If you follow the following will fix the problem:
1. Open file explorer
2. Open local disk C: (If this is where solidWorks has been saved, generic location)
3. Open program files
4. Open SolidWorks Corp
5. Open SolidWorks
6. Open lang
7. Open English
8. Scroll down until you see gtol97.sym
9. Rename the file Gtol.sym
10. You must restart SolidWorks to take effect, once open all dimensions will show the Ø in drawing sheet.
11. Have a cup of coffee and smile
RandallDesigns - 3D CAD Design Dorset