I did not manage to find Ledger’s article, but it seems to me that they implemented noise during cryptographic operations, Seed signer could do the same thing if it is not already integrated.

My first thought is that b/c with SeedSigner you're dealing with words/QRs that represent your PK, your surroundings and potential video surveillance should already be front of mind. But as to your specific question, haven't thought a ton about this threat and am not aware of any specific countermeasures out there.