An apparatus (10, 240, 300) includes a signpost (11, 241-256, 322, 612, 623, 626-628, 652, 661, 682, 686, 703) which transmits signpost signals (24) that are received by a tag (12, 271-275, 301-316, 395-397, 616-618, 641-643, 653, 656-657, 662-664, 679, 708, 711). The tag in turn transmits
radio frequency beacon signals (72) which are received by a reader (13, 261, 319, 521-530) The tag can vary the duration of the
beacon signals, for example in dependence on whether it is currently receiving a signpost
signal. Further, the tag can dynamically vary the
transmission rate and / or transmission power of the
beacon signals, for example following
receipt of a signpost
signal. Varying these parameters can facilitate compliance with governmental regulations.