You probably have a laptop computer. This symbol is telling you that the "NumLocks" are currently enabled. On a regular keyboard, this will change the numeric keypad from typing numbers to typing the arrows (plus home, end, PgUp, PgDn, etc). On a laptop, this causes the keys with numbers above/below them (j, k, l, etc) to type the numbers instead of the letters.
Simply hit the NumLock key to change this setting.
HTH,
JW