Search for secondary studies is essential to establish whether the review on the intended topic has already been done, avoiding waste time. In addition, secondary studies are the inputs of a tertiary study. However, one critical step in searching for secondary studies is to elaborate a search string. The main goal of this work is to analyze search strings to establish directions to better detect secondary studies in Software Engineering (SE). We analyzed seven tertiary studies under two perspectives{:} (1) structure - strings’ terms to detect secondary studies; and (2) field{:} where searching - titles alone or abstracts alone or titles and abstracts together, among others. We also performed a validation of the results found. The suitable search string for finding secondary studies in SE contain the terms “systematic review”, “literature review”, “systematic mapping”, “mapping study”, “systematic map”, “meta-analysis”, “survey” and “literature analysis”. Furthermore, we recommend (1) researchers use the title, abstract and keywords search fields in their searches to increase studies recall; (2) researchers choose carefully their paper title, abstract and keyword terms to increase the chance of having such studies found on digital libraries.