I am not familiar with such a universal dictionary symbol. Have you tried looking in the front (or back) of this dictionary? There might be a listings of symbols it uses. If anything, this looks like a macron. If you can't find such a symbol listing in your dictionary, please let me know and I'll ask other foreign language experts. And if you find out more about this universal dictionary symbol, please share! I'd love to learn about it.
--Joanna