The v-string is just a convenient way for the programmer to construct a literal string composed of (possibly) non-printable characters.

$string = v1.2.42;

# or

$string = 1.2.42;

# is just an easier way of writing:

$string = "\x01\x02\x2a";
[download]

It doesn't matter how the programmer using your code wrote the string expression, the result is the same. If your code expects a string limited to a certain subset of characters, then you should validate the input.