The system that is processing the input data has to be able to
distinguish between noise, dots, commas and symbol annotations, for
example: A' and 
.
If the information is noise, then it
must be removed from consideration. However, removing something which
is an annotation must be avoided. This is a more significant problem
in the processing of scanned input, as noise is likely to arise from
the scanning. Online input with a pen and tablet is not as
susceptible, unless you want to account for a user accidentally
tapping on the tablet with the pen and drawing odd dots and lines.
This does not occur very often, and it's easy enough for the user to
notice that they have done so and let them either undo or delete the
mistake themselves.