I'm not entirely sure this is an adequate question on this site since it's not a mathematical but rather a language-related one, but I've been wondering about this for a while. I'm sure we all agree that when presenting a mathematical proof, one should first clearly state the statement to be shown.
In German, one uses the conventional notation is "z.z.:" to indicate that the problem statement begins, which is short for "zu zeigen" = "to be shown". It's a useful little abbreviation and I was wondering if anything similar exists in conventional mathematical notation in English, since I haven't come across anything like it yet.
There is wts for want to show and nts for need to show, but they are not as common as zz in German and perhaps even more informal.
They both appear in this Wikipedia entry on mathematical jargon.