Dow Jones v Transportation Index is one that I follow very closely. It can show problems emerging in the economy well ahead of the overall market.
Dow Jones Index v Transportation Index weekly. Sometimes transports lead the market and sometimes they lag the market. What we know from looking at this chart is that the upside in the Dow Jones is likely to be limited at best. A turn from over sold in the Dow and Transports can also be a very good dip buying opportunity in stocks.
FDX daily. This is one of my bellwether stocks. It has broken this long term ascending wedge. It is not on my month swing high yet but could be a candidate for early 2018 the way things are looking.