When counting characters (or "chars") the proper term used in German is not Zeichen but
which counts also the blanks (whereas Zeichen is sometimes understood to count only visible signs). The word Anschlag/Anschläge is related to the old cultural technique of typing on typewriters. One hit on a key is called Anschlag, and this usually comes with a carriage move by one step. (Interesting exception: hitting a key for diacritics such as on à, á, â. Such diacritical keys do not cause the carriage to move.)
You may abbreviate Anschläge as
which will be broadly understood by native speakers, at least those with some acquaintance with cultural techniques of writing and publishing.
But of course it looks silly. Abbreviations that save you three letters of nine, and add a dot, so you end up with a net win of two, are just not justifiable.
Corner for experiments
By the way, as Anschläge bears the amibiguity of "do you mean hits on keys including those for diacritics, or do you mean carriage steps", a more precise term would actually be
but that's a word I never heard being used. It may have been used by typewriter engineers, but this is just what I suppose.