Tokens (also called Assets) can have an arbitrary divisibility from zero up to eight decimals. While Amount is meant to be used for and fixed to eight decimals, another - more generic - value object class for arbitrary decimals is needed: ChainValue
Token amounts are called quantities and the always returns the token quantities the suffix QNT. See an example here
So, a Token FOO can have four decimals, which would result in
1 FOO = 10,000 FOOQNT 1 FOOQNT = 0.0001 FOO
Similar to Amount SignumJS provides a value object class calls ChainValue and allows to convert and calculate with quantities.