It is about steareochemistry. That's what you asked I guess.

dextrorotary compound = sign is (+) or "d"

levorotary compound = sign is (−) or "l"

https://en.wikipedia.org/wiki/Catechin

Thanks alot .. 

Gallocatechin or gallocatechol (synonyms) has two chiral centres at positions 2 and 3, and thus four diastereoisomers. This is the same as with catechin. Gallocatechin has one more hydroxyl group at the B ring than catechin.

(+)-Gallocatechin is (2R,3S)-2-(3,4,5-Trihydroxyphenyl)-3,5,7-chromanetriol

(-)-Gallocatechin is (2S,3R)-2-(3,4,5-Trihydroxyphenyl)-3,5,7-chromanetriol

(+)-Epigallocatechin is (2S,3S)-2-(3,4,5-Trihydroxyphenyl)-3,5,7-chromanetriol

(-)-Epigallocatechin is (2R,3R)-2-(3,4,5-Trihydroxyphenyl)-3,5,7-chromanetriol

http://www.chemspider.com/Chemical-Structure.58594.html?rid=bf2ed37f-5690-4ec6-aa9e-5f2c925b8bbf

http://www.chemspider.com/Chemical-Structure.8600662.html?rid=b8300988-7d05-4d40-9e8f-6611dd716c3e

http://www.chemspider.com/Chemical-Structure.8600662.html?rid=ec32aea4-336f-487e-bb3b-1be7a6a01ca8

http://www.chemspider.com/Chemical-Structure.65231.html

Your links are super informative Andrea, thanks!..

(+)-Gallocatechin is (2R,3S)-2-(3,4,5-Trihydroxyphenyl)-3,5,7-chromanetriol

(-)-Gallocatechin is (2S,3R)-2-(3,4,5-Trihydroxyphenyl)-3,5,7-chromanetriol

(+)-Epigallocatechin is (2S,3S)-2-(3,4,5-Trihydroxyphenyl)-3,5,7-chromanetriol

(-)-Epigallocatechin is (2R,3R)-2-(3,4,5-Trihydroxyphenyl)-3,5,7-chromanetriol

(+)  (-)- mention stereo isomer

the best answer is 

Andreas Josef Schwab · 37.77 · 409.91 · McGill University

I agree with Charles Antony's answer.

- & + signs indicate stereo isomers

The two Gallocatechins and the two epi Gallocatechins indicated by Andreas Josef Schwab must be enantiomers or mirror image molecules that cannot be separated via achiral chromatography. On the other hand the Gallocatechins must easily separate from epiGallocatechins even in achiral chromatographysince they are diastereoisomers.