Here is a list of a few that I find to be of most value:Population TotalHome ValuesHousehold IncomesPoverty RatePopulation AgeRental Vacancy Rate*Homeowner Vacancy Rate*Educational Attainment Rate (High School/GED & Bachelors)Number of Housing UnitRent to Income Ratio*Rent to Price Ratio*Population on SNAPS (supplemental nutrition assistance program) percentageProperty Tax Rate*Median Age of BuildingsNumber of Structures by Units (SFR, Duplex, Triplex, Quadplex, etc...)Median Rents by Number of BedroomsPopulation Change (Births, Deaths, In-Migrations, Immigrants)  *note that some of the metrics are composites that are computed by comparing two or more variables from the ACSA number of the variables above can also be broken up into cohorts, which will give you even more insight into how an area is doing.

Owners visiting their vacation properties and finding lots of missing items, broken furniture, and just run properties. 

@Rahul Handa Our 8 plex got sued last year (slip and fall on ice in the parking lot, broken hip).

This is one for the history books: He has locked himself out and broken down the door/ created a hostile living environment for the other tenant/ had the police officers at his apartment 4 times in 1 week/ has a restraining order against a ''lady he picked up off the street" who now lives with him. 

Many have a realtor assigned to them and you can get in that way. if you’re in a freezing area then I usually figure on broken pipes.

Just with broken down fixers, a investor has a ton more negotiation power and more flow of investors rather than a particular purchaser.  

Again, for someone who doesn't want to have their pockets broken (who does?)

This is interesting - a kind of "heat map" showing where most of the construction activity is taking place in Philly, broken down by neighborhoods:Construction Permits in PhillyArticle explaining it here: Mapping Gentrification in Philly by Tracking Building Permits

We have already spent money repairing different things that have broken, and make some small improvements (About 6k so far). 

My favorite anecdotal predictor of neighborhoods turning for the better is a local brewery opening up shop in a formerly vacant warehouse space (think abandoned, broken windows, homeless hangout type of warehouse).