You shouldn't ignore them, but you should show that you know it's safe to go/proceed etc. as well - don't just purely rely on what they do.
Sometimes looking out for vehicles doing this is actually a necessity - for example, large vehicles turning into junctions from which you're emerging. They'll often flash you to let you out so they can fit into the junction (i.e. they'll stop the flow of traffic and wait for you to emerge before proceeding). If you miss that kind of signal, you'll be sitting and waiting for a long time
So in short: Don't ignore them, but don't blindly follow them either. Think.