I'm sure i've been asked the question before and that the answer is No, as there is no variable in the reporting layer to see who is logged on to Sage.  I've had another look and i cant see anything at all so i'd say no.

Yes, it has been asked before: https://www.sagecity.com/gb/sage-200cloud-uk/i/sage-200cloud-uk-ideas/ability-to-add-the-windows-username-onto-a-report-or-layout

Anyway, I did a small add-on that adds the current Windows user name to the SYSCompany table in the data model, so it can be added to reports.  Download it from http://www.gandb.plus.com/gtsagedev/sageforum/UserName.sdbx