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Cognitive radio is a promising solution to the problem of spectrum scarcity by means of allowing secondary radio networks access the spectrum opportunistically. One of the most important issues in cognitive radio is how to detect existing over-the-air signals reliably. Not a few literatures have reported that signals could be detected via their inherent or embedded properties. However, these may not be reliable and flexible enough for all kinds of signals with different modulation types. In this paper, we propose a multitone beacon signal carrying cyclostationary signatures, which is able to strengthen the reliability and efficiency of signal detection at low cost of spectrum overhead. This beacon not only can indicate the presence or absence of user signal but also can reveal some other information helpful to opportunistic spectrum access through the bit word modulated in its cyclostationary signatures. It could be applied to device/network identification, indication of spectrum allocation and spectrum rendezvous, both for primary and secondary users. The generation and detection algorithm of the beacon signal are presented firstly in this paper, then an initial simulation analysis and experiments with radio devices are illustrated to discuss the performance.