Okay, so as we all know, yowies are attracted to noises. Whistling, etc. Even the noise of a baby crying. So, an idea sprang to mind. All you'd need is a cheap tape recorder with an inbuilt speaker & sand. Simply record various sounds (crying, talking, whistling, laughter; whatever comes to mind) & leave the recorder in the middle of a patch of sand. Maybe cover it in a plastic bag so perchance it rains it won't die on you.
But either way, if they are around your area, they'll come up and have a look at this thing thats making noises. Hopefully even step on the sand. Which in that case, you have yourself a footprint - which would lead to the conclusion that you've got yourself "friends" in the area. Try and mix and match up the sounds. Hell, even leave an apple or something there. Gives them more incentive to have a good look.
(I say cheap tape recorder because, well, one might get angry and smash it to pieces
