bistefano Dec 5, 2012:

Yes, I have no doubt that シェア7.29％ means "Market share" and not ownership as you say (I just wrote "share" without thinking about the possible ambiguity).
On the point of ▲ vs. ▼, your new reference from Teikaku bank, coupled with your in-field experience, makes me reconsider my previous position ... though I'm not reversing my statement in regard for instance to scientific or mathematical papers, I'm now inclined to believe on your authority that this is indeed a special usage in accounting and not an error/misprint.
Thank you for the thorough and interesting discussion.
Best wishes

T.B. Dec 4, 2012:

@bistefano The meanings of those triangle signs are well known among people like accountants. Since I didn’t have an accounting text book to scan and upload to the site for reference, I posted that damn URL, which was only one I could find online. The term seemed to be from the Teikoku Databank survey (see links below), in which various banks, credit unions and such were ranked according to the number of firms that financially rely on each of them. “Share” is the percentage of the bank industry in that case, not an ownership interest in a corporation.
http://www.tdb.co.jp/report/watching/press/p121105.html
http://www.tdb.co.jp/report/watching/press/pdf/p121105.pdf

bistefano Dec 4, 2012:

I have looked up your ref. at http://oshiete.goo.ne.jp/qa/5151808.html and it is a Q (question) - if you read down the A (answer) which follows in the same page, it is stated that for 赤字 the sign goes like マイナスの場合、▼１２３
Besides, I wouldn't take a question-answer page between peoples on a generalistic portal like that as an authoritative source.
The question than is whether the filled sign ▲ is equivalent to ▼ or to △ .
I maintain that it means △, as I just said.
The filling could be an artifact, error or whatever.
Of course, more data/context on the page could well provide the right answer to this.