What is the proper abbreviation for the test statistic in Wilcoxon signed rank test? What is the APA conforming symbol for the test statistic from the Wilcoxon signed rank test?
Different statistics software outputs all kinds of letters from V to Z.
I thought it was W?
 A: As a general thing (regarding your title), there's no "proper" abbreviation, as the plethora of symbols suggests. 
In his 1945 paper, Wilcoxon doesn't seem to use any symbol for the signed rank statistic at all (he does at one point use $T$ for the rank-sum statistic). If he had, that would be the closest to 'proper'. Most commonly, W seems to be used, but it depends on what you read. T is also pretty common, but in any case many (most?) treatments use a different (but equivalent*) statistic to Wilcoxon's 1945 original.
* in the sense of leading to rejection of or failing to reject the same samples under the same conditions
As for the body of your post (referencing APA guidelines), short of reading the style guidelines themselves (an admittedly onerous task), one approach is to find a few papers discussing the signed rank test in a journal that follows the APA guidelines. If there is such an 'APA-conforming symbol', presumably they will all be the expected one, and if there isn't, you have at least one symbol that would seem to be acceptable.
