ASCII has no code points beyond 127, so it is not ASCII. It is compatible with IBM CP437, which is essentially obsolete, although might be used in Windows DOS boxes.
Typical modern systems, in the USA and Western Europe, use the ISO 8859-1 encoding, in which the code point would be 251, although there is an increasing trend towards using UTF-8, in which it would be represented by the two byte sequence. This forum uses UTF-8.
The encoding you are actually reading out will depend on the OS you are using and how it is configured, as well as the configuration of any terminal program you are using. These are essential things to know if using characters outside the 95 character ASCII printable range (counting space as printable), and nothing to do with Asterisk.
If you read out 164 as ISO 8859-1, you would see an uncommon currency symbol, consisting of a small, centered circle, with spikes pointing out in NE, SE, SW and SE directions (assuming North is up). That is not what you posted to the forum, though. That character is “¤”, although I cannot guarantee that your system will reproduce it.
Interpreted as UTF-8 it is an invalid first byte of a code, so would presumably produce some form of error recovery action.
My best guess is you are writing it as CP437, and you are seeing the results of error recovery from trying interpret it as invalid UTF-8, with Asterisk not changing it at all.