Actually 3rd edition Magic in the Shadows does cover it on pg 58
QUOTE ( MitS pg 58)
Upon a character's first initiation, full magicians receive
access to the metaplanes of astral space (see Metaplanes, p. 91). In addition, an initiate can
choose one of the following three advantages during each initiation. The first option is to raise
the initiate's Magic Attribute and learn a metamagical technique. The second option is to raise the
initiate's Magic Attribute and alter the initiate's astral signature. The third option is to shed a
geas. Only one of these options may be chosen when a character initiates.
So by foregoing the metamagic they would have gained at that initiation, a mage could alter their signature so previously gathered/learned material links/signatures would no longer work/trace back to them.
Later on in 4th they introduced the Flexible Signature Metamagic, which allowed a mage to alter their signature at will, pretty much replacing the option above.
QUOTE (SR4)
• Flexible Signature: The initiate can choose to alter her astral signature
(p. 192) at will, disguising it so that it cannot be used to
identify her, forging the astral signature of another magician, or
simply reducing the amount of time her signatures last.
When someone attempts to assense a faked signature, add
the faking magician’s initiate grade to the Assensing Test threshold.
So if a grade 2 initiate leaves a forged astral signature, another
magician would need to score only 3 hits as usual to see the fake
signature, but would need 5 hits to realize the signature was fake
and spot the true signature hiding underneath. The initiate must
have assensed someone else’s astral signature in order to forge it.
Initiates with this metamagic can also reduce the longevity
of astral signatures they leave behind by the initiate’s grade
in hours. So a grade 3 initiate can choose to leave no signature
on Force 3 or lesser effects, and the signature of a Force 5 effect
would last only 2 hours.
.
So a smart mage with this would alter their sig before going out on a run so as to leave a false trail or very little trail from the scene.