can specific heat used to identify substances? how?

Answer 1

Yes of course, theoretically, every element has its own specific heat, see link.
A scale and a calorimeter would do it.
Now when you go beyond the elements into general substances then your screwed because of the high number of combinations.

Answer 2

Any property can be used to characterise, but specific heat seems rather inconvenient, non-specific, and of no use for unknown mixtures.

Historically, it is very important. The Dulong-Petit Law (see e.g. Wikipedia for this) states that the gram specific heat of any solid is 3R/M, where M is molar mass. This because each particle has 6 degrees of freedom, and it is valid at temperatures high enough for quantum effects on specific heat not to matter too much. So in the late 19c, when new elements were being identified, this rule gave approximate atomic masses, good enough to decide whether the oxide (say) was MO, M2O3, or MO2.