The default left and right triangle icons (as used in the calender block to move to the previous or next month and as a seperator in the breadcrumb trail) have issues on Android.

On Android 4.0 up, the font is called Roboto. It seems to not have the left pointing version.

I've not seen it myself but I've had reports that 2.3 devices (which use a font called Droid Sans) are missing both versions.

Here's a list of the geometric shapes available in Unicode:

http://www.alanwood.net/unicode/geometric_shapes.html

We currently use:

25BA BLACK RIGHT-POINTING POINTER
25C4 BLACK LEFT-POINTING POINTER

I believe these particular shapes may have been originally chosen to ensure they displayed on IE6/XP (IE6 has issues where it didn't fall back if the first chosen font didn't contain the character, proper browsers continue to search through all your fonts).

Perhaps a different triangle shape could be used? Though testing that it works on everything else could be a pain.

Longer term these could be provided by an icon font or SVG icons.

I'm marking this as RTL-related as I assume the left facing one is used more in those situations, and at least on Android 4.0 that seems to be the main issue.