Abstract: A telltale structure which includes an elongate base tape with a pressure sensitive adhesive coating on the inner surface to engage the surface of an object to be studied.Bonded to the outer surface of the base tape is an elongate overlay tape which contains a plurality of longitudinally spaced apertures.Captured between the juxtaposed portion of the tapes are the inner end portions of thin, flexible streamers which have the free outer portions thereof within the confines of the apertures, whereby said outer portions can be acted upon by a fluid medium flowing over the surface of the object to be studied.In producing the telltale structure, a continuous length of streamer material is laminated between the two tapes to provide streamer portions which are exposed in the apertures in the overlay tape, and one end of each exposed portion is then severed to provide the aforesaid free outer portions.