simple Rule

When Corporate spreads are below moving average, probably going down you make the most money in equities when it's above like now it starts to be dicey. I will pay attention to this.

but sometimes this is an early signal 

in 2002 spreads were starting to go down because economy was in trouble and stocks lost 23% (s&p )
spreads start going up in 2006 and 2006 was still ok equities up 13%
spreads are going up in 2018 and i think it's still ok