Is it not very likely that most of the material that could contain possible biosignatures, like clays and carbonate containing minerals, will be below a layer of dust or regolith on Mars ?
That the material the rover can examine on the surface is 'only' the top of the iceberg ?
The RIMFAX radar imager onboard Perseverance could help in localizing such material below the surface.
But because of the low gravity on Mars, digging to the possible biosignatures would be difficult because a traditional excavator would not provide enough reaction force to penetrate into the regolith.
Credits: NASA Kennedy Space Center
From this article:
RASSOR uses counterrotating bucket drums on opposing arms to provide near-zero horizontal and minimal vertical net reaction force so that excavation is not reliant on the traction or weight of the mobility system to provide a reaction force to counteract the excavation force in low-gravity environments.
Credits: NASA/Kim Shiflett
On the image above from this article you can see the scoops around the circumference of the cylinders.
So with some modifications, like brushes on the drums to remove the lowest part of a dust or regolith layer from a layer with possible biosignatures, would RASSOR not be very suitable to assist Perseverance ?