Over the last years, there has been a lively discussion whether (automated) vehicles should be equipped with novel external human-machine-interfaces (eHMIs) in order to facilitate communication with nearby vulnerable road users. This exploratory study investigated whether the introduction of eHMI-equipped vehicles to public traffic potentially influences how pedestrians interact with vehicles without eHMIs. To that goal, our participants specified their willingness to cross in front of vehicles that were either equipped with a frontal brake light eHMI or not in a video-based experiment. Between groups, the quota of eHMI-equipped vehicles in simulated traffic was varied. Our findings show that the quota of vehicles with an eHMI did indeed influence street crossing willingness in front of yielding as well as non-yielding vehicles without an eHMI. Notably, the magnitude and direction of the effect was dependent on the distance between vehicle and pedestrian. Future research on eHMIs should take potential unintended side effects of eHMIs into account.