The aim of this paper is to show that the fuzzy signature model based on non-destructive in-situ measurements and visual inspection can be used to obtain equally reliable results on the strength of masonry as destructive tests. The fuzzy signature model was constructed to describe a masonry based on different measurements of. The aggregations of the signature were given as weighted geometric means. Weights of the input values of the aggregations were determined by two different optimization methods: (i) an iteration procedure was chosen, which showed significant differences in the result; (ii) a genetic algorithm was used, which produced similar but more accurate approximations to the results of the destructive tests. The comparison of the two optimization results gave new conclusions that are valuable information for the further development.