The easier way would be to use the replace field contents menu item/script step. Use the last radio button that says "Replace with calculated result:" and use some calculation like this:
If(YourTable::YourField = ""; "YourSymbol"; YourTable::YourField)
What this does is put the symbol ONLY is the field is empty, otherwise, it leaves it with its current content.
Then click ok. With this, you wouldn't even have to do a find.