Hi!
There are only 73 entries (including some duplicates) showing up for a straight P249 search, which is a bit strange in any case -
https://query.wikidata.org/#SELECT%20%3Fitem%20%20%3Fstock%20WHERE%20%7B%0A%...
Sampling a few items suggests that most businesses don't use P249 directly, instead they use it as a qualifier on P414, eg https://www.wikidata.org/wiki/Q156578 or https://www.wikidata.org/wiki/Q156238
You can use something like this: http://tinyurl.com/hdoqrjt
The key thing there is UNION - that's how you do "this or that".
Note though ticker symbols are not unique (they are per exchange) so you may want to either group: http://tinyurl.com/jmbrf4p or add stock exchange name to it or do something else, depending on your case.