Unicode arrows heads:
- ▲ - U+25B2 BLACK UP-POINTING TRIANGLE
- ▼ - U+25BC BLACK DOWN-POINTING TRIANGLE
- ▴ - U+25B4 SMALL BLACK UP-POINTING TRIANGLE
- ▾ - U+25BE SMALL BLACK DOWN-POINTING TRIANGLE
For ▲ and ▼ use
▼ respectively if you cannot include Unicode characters directly (use UTF-8!).
Note that the font support for the smaller versions is not as good. Better to use the large versions in smaller font.
More Unicode arrows are at:
Lastly, these arrows are not ASCII, including ↑ and ↓: they are Unicode.