Unmistakeable if the entire organ is visible in the field of view (low power), appearing as a misshapen, two-tones fruit, complete with stem. In some slides, the combination of red, whitish, and blue stained regions is also distinctive.
The thyroid gland is the only slide you will see in which larger circular structures (follicles, 1) are filled with a uniformly pink staining substance, the colloid (2).
Look for a multilayered effect, with several layers of different "textures" due to differing arrangements of cells. Lacks the tubular or circular structures seen in many of the other slides. At low power the gland may often (but not always) appear roughly triangular.
Extensive, small, dense clusters of cells with occasional larger clusters of lighter staining cells.