In response to previous tip: With the standard tools it isn't possible to generate a where-used list of tables, strings, standard texts etc.. in SAPscript forms. Therefore I wrote the report ZSEARCH_ITEMS_IN_SAPSCRIPT.
A quick approach to searching for strings (not exactly a where-used list ... just a textual search) is to choose Utilities -> Form info and then press the find icon. You will still need to drill into specific instances to see where they are, but it is usually sufficient for me. Enjoy.