Air carrier pilot reported a safety concern regarding incomplete NOTAM language at BGR airport Runway 33 where the takeoff point on the runway is displaced due to construction but not stated clearly in the NOTAM; airport signage; or through ATC instruction. Reporter also stated this could impact the safety of construction workers.

Narrative

Runway 33 is currently shortened and NOTAM'd as such. The closed portion of the runway is clearly identified; and the threshold is further displaced. There are threshold markings and lights as well as PAPI indicators appropriate to the displaced threshold. Arrival was uneventful.Access to runway for takeoff is via Taxiway K. At the hold point; there is an orange sign indicating TORA (Takeoff Run Available); TODA (Takeoff Distance Available); ASDA (Accelerate Stop Distance Available); LDA (Landing Distance Available); all with the exact same value. Performance data and NOTAMs are for this value as well. The displaced threshold is several hundred feet northwest of this runway entry point; yet all four values are the same. Thus; the actual takeoff point for the runway is at the displaced threshold point since all four distances are exactly the same. However; this is not indicated in any way; not by NOTAM; controller direction; or sign. Aircraft Y that departed ahead of us applied takeoff thrust at the runway entry point; not downfield at the start of the usable takeoff runway point. We subsequently questioned the controller; who said; Yeah; the City doesn't want people starting takeoff at K; but it hasn't been working out too well." Seems as if the workers on the portion of the runway under construction could be endangered because the start of the usable takeoff portion of the runway is not clearly identified.Risk could be mitigated with a lighted sign; clarified NOTAM; or controller instruction. Not dissimilar to [Runway] XXL at ZZZ; just a longer distance."