Pictured below is an excerpt from Sibelius’s Tapiola, (Bar 460):
It looks to me like a trill/mordent on its side, to fit into the condensed score. But is it?
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It's rests for separate voices. If you got a "div." for the passage at some place before, the violin I section is divided into two groups playing two voices.
If not, you start playing an E5 on the A string on beat 1, then tilt the bow on beat 2 to play the same note on the E string as well. Rinse, repeat. Two voices on a single instrument. The second bar, however, makes this interpretation rather unlikely since it would require distributing the voices across D and A string in a manner and positions that are unlikely to sound good in an orchestral setting.