请问手机按键上的井号如何翻译?

电话上的叫"POUND SIGN"
In the United States of America, the symbol is traditionally called the pound sign. It derives from a series of abbreviations for pound avoirdupois.

其他场合叫"NUMBER SIGN"

number sign

没想象的那样复杂，直接说 "#" Key 就行了。

i guess
double cross key