Is there any standard?

From Wikipedia [1]:

"""
Note that 96 ("`" grave accent) is a character that is seen in uuencoded files but is typically only used to signify a 0-length line, usually at the end of a file. It will never naturally occur in the actual converted data since it is outside the range of 32 to 95. The sole exception to this is that some uuencoding programs use the grave accent to signify padding bytes instead of a space. However, the character used for the padding byte is not standardized, so either is a possibility.
"""

This obviously makes impossible using "`" as zero instead of space.

[1] https://en.wikipedia.org/wiki/Uuencoding#Uuencode_table