Unfortunately not all brokers are safe. Most brokers that offer no deposit bonuses are not trusted. That is why it is really important to only choose a broker that is reputed & well regulated. If a regulated & popular broker is offering No deposit bonus then there are lesser risks.
As per our check XM Broker, FXOpen are brokers that are regulated with at-least 1 Top Tier regulator & offer no deposit bonus. But you should still carefully read terms of these brokers before signing up for any of their bonus.