Yes, IBM had a specific set of symbols.
Actually all the characters were 8-bit, but the plain ASCII characters all have their high bit set to 0. IBM simply specified what symbols displayed when the high bit was set to 1.
I don't remember exactly what that symbol set was (would have to search for it) but most character sets show some set of symbols for the high-bit characters, so if nothing shows something must be stripping the high bit (some programs used to do that).