What indicators do investors really look for that lets you know whether the market is up, down, or trending in a certain direction? How can you tell?

All depends on what your investment goals are. If you are flipper you will look at different metrics compared to buy and hold investors. Personally, I don't look at any metrics to figure out the market trend. I am a buy and hold investor so I just continue to buy a property every 6 months.

@Darryl Jennings

Here are some of the metrics that I find valuable to understand:

- Population

- Home Values

- Household Incomes

- Rental Vacancy Rate

- Homeowner Vacancy Rate

- Poverty Rate

- Educational Attainment Rate (High School/GED & Bachelors)

- Number of Housing Unit

- Rent to Income Ratio

- Rent to Price Ratio

- Population on SNAPS (supplemental nutrition assistance program) percentage

- Property Tax Rate

- Median Age of Buildings

- Number of Structures by Units (SFR, Duplex, Triplex, Quadplex, etc...)

- Median Rents by Number of Bedrooms

- Unemployment Rate

- Employment Sectors Percentages

These are just some of the indicators that will help you understand the quality of an area as well as the kinds of returns one is to except.

By taking into consideration the direction in which each of these metrics are trending, you will better understand where the market a whole may be heading.

It's also important to also analyze the various sub-markets that make up major markets. These will often vary to a high degree from the averages a general market analysis will yield and possible help you uncover hidden opportunity. 

Hope this helps!