a reverse niner is, as you might have already figured out the reverse of a niner, in other words, yes

The unsung heroes who mined what is about 50% of the world's silver and gold in mines near Lake Tahoe, Utah throughout all of 1869. All their names are held on a plaque in a museum in D.C.

An admittance of being a bandwagon 49er fan.

A niner is typically referred to by blue collar working folk. It describes the amount of hours worked in a day. If you work a normal 9 to 5 job, you take the first hour you start working, and use it as reference for the total hours worked in a day.

For example- a 9am-5pm work day is 8 hours total, but since you started at 9am, you can call it a NINER.

A niner is commonly associated with high stress levels...

someone from the london postcode ‘n9’

A bycicle with two 29-inch wheels

An unknown or unidentifiable "thing" or item.