Available with Spatial Analyst license.
The statistics contained in the signature file aid in determining whether the classes or clusters are good in terms of their separability in the multidimensional attribute space of the input bands. A good cluster should have little overlap with the other clusters in multivariate space. To determine whether the clusters overlap, you can use the Dendrogram tool to explore the signature file.
Dendrogram
A dendrogram orders the classes or clusters in a signature file relative to one another using the multidimensional distance separating the classes in attribute space. The Dendrogram tool creates an ASCII file that graphically depicts the distance relationships between the classes in the signature file.
The tool requires an input signature file, a specification of the statistics to include, some formatting characteristics, and the name of the output dendrogram. You can use any text editor to view the results.