Symbol files are debug information about an assembled rom.
A symbols(*.sym) file is a binary format that contains a series of symbols in the format: an absolute addresses, where the first byte is the most significan byte, the second is the least significant byte, followed by a null-terminated string. They are generated by Uxntal assemblers, such as Drifblim, and are used by debugging tools, such as Beetbug, which do not otherwise have access to a program's labels.
0140 on-draw 0142 on-draw/loop 01a8 clip-tile 01f2 ...
incoming drifblim beetbug