The article is devoted to the consideration of problematic situations that may arise when determining interfering factors (natural, artificial) when in the investigated signature their combined effect manifests itself or the presence of the same information content under the influence of various interfering factors is found.
Considering the possibility of such complex cases arising from the ambiguity of the origin of interfering factors, with insufficient information content of the signature, an insignificant number of free samples identifying features that prevailed over others, the ability to explain the differences and the lack of full confidence in the categorical expert is a probable form of conclusion.
To sum up it can be concluded that handwriting experts obtain scientific research on the identification of interfering factors affecting the signer. The level of knowledge and experience of the expert, the perfection of research methods, etc. will play an important role.
Key words: signature, interfering factors, natural, artificial.