No, the junk bonds market is not any real true indicator of the stock market's future. I feel like the junk bonds market is a small piece of the puzzle when it comes to the entire picture of the stock market. It can not be used as a true gauge in my opinion, but merely as a suggestion.
There has been much speculation that the junk bonds market is tied to the stock market and offers a glimpse into the future. While the brokers sometimes can spot trends between the two markets, rarely can anyone adequately predict the future of the stock market solely by watching the junk bonds market. Instead, to find the true indicator of the future for the stock market many aspects need to be considered.
Junk bonds are a bit of a market indicator, but should not be used as a true and important factor in trying to anticipate the future of the stock market. Interest rate changes will affect junk bonds and the stock market, but just because they would both be affected doesn't mean they will respond in the same way.
I think that this is a case where correlation does not equal causation. I think there is a weak association between a junk bond swing and a full economic downturn. I think it is always good to look at all aspects of the market before buying and selling but I wouldn't solely decide based on this.