Does a similarity coefficient of -0.93 mean that two things are similar or dissimilar?

Unsure and unknown, like EVERY statistical generalization. The exception to the generalization can have a deviance of one to twenty percent, to be legitimate in some professional situations. In a manufacturing process, a low-quality manufacturer (1945: Japan; 1985: Taiwan; 2005: Korea; 2011: China) might suggest that 0.93 is similar.