According to some embodiments, there is provided a Collective Perception Message, CPM, characterizing a plurality of Vulnerable Road Users based on a plurality of received VAMs, thereby allowing an ITS station to efficiently aggregate VAM messages from VRUs and retransmit information about the VRUs to other ITS stations. Consequently, the security is improved as some ITS stations may not be able to detect or identify VRU stations by themselves but thanks to the CPM, these stations can still be informed of the VRUs. According to other aspects, congestion is avoided while maintaining safety vis-à-vis VRUs thanks to the use of a different transmission scheme when the VRU is already characterized in a CPM sent to the ITS stations. Also, a receiving station can evaluate whether the content of a CPM can be trusted or not. Safety is thus improved. This is achieved thanks to the CPM that references a certificate.