Every major building, and most organizations, have a number of 'faceless' functionaries that handle infrastructure tasks. Janitors, building superintendents, maintenance personnel. These people are not expected to interact with the public. Blank looks and mumbled answers are the expected response if confronted. When in doubt adopt a vague, disinterested, blank look. Remember that the highlight of your days are quitting time and payday. Which works out because you are often not going to have enough information to give a detailed response.

A clipboard and stack of official looking forms, particularly vague 'work orders', and a picture ID from a company with a completely opaque name, like Universal Logistics and Management, helps sell it. Presenting yourself as an outside contractor offers an excuse for a lack of local knowledge.