I have "Emax Motor-cf2812- 1534KV" and "Emax ESC-25 Amp" for my RC Glider plane. There are no markings of positive (+) and negative (-) on both ESC and MOTOR to connect each other.
Here I have attached Photograph of ESC and MOTOR. Wires of ESC mark as A, B, C. and wires of MOTOR mark as 1, 2, 3. 
Can you guide me how will I identify positive (+) and negative (-)?  Or how will I connect A,B,C to 1,2,3 ?

Sir there is no polarity. just connect  a-1,b-2,c-3  and check the direction of rotaion.if you want to reverse rotation swap any two wires.

@jp,
You got your answer within 5 minutes!

Please use bullet connectors (see pic) if you have them. Males on motor, females on ESC.
Makes it easy to swap two wires (and to separate ESC from motor).

Two important things to keep in mind:
1. Soldering quality has to be excellent, (to bullets or direct), else motor will give trouble.
2. MUST use heat shrink tube to avoid contact between wires. Or at least electrical tape.

Safe way to solder bullets is to drill holes in a wood block, insert bullets, heat with a soldering iron, fill with solder, dip wire in solder and hold steady till cooled. Joint must remain shiny, if it goes dull the soldering is not good enough, and needs to be redone.

Just trying to help, so please don't mind if you already know all this stuff.

Best of luck.

.