android - Unicode character fallback?

Certain mobile browsers do not seem to support all unicode characters, like this down arrow icon:

span.icon:after {
    content:"\25be";
}

Simply nothing is displayed. How can I detect this and provide either fallback text or an image?

Answer

I'm not sure about fallback, but you may want to try

content:"\25bc"
(larger arrow)
instead of
content:"\25be"
It is said to be better supported.
See also https://stackoverflow.com/a/2701226