What's the signifigance of 'Marking' my Pokémon?

Question

When I go into the PC and select a Pokémon an option comes up titled "MARKING". It gives the options of a circle, triangle, square, heart, star or diamond. Is there any meaning to these symbols?

Answer 1

Markings

>A marking tool was introduced in the Generation III games,
> with Lanette's Pokémon Storage System. This tool helps the player to
> organize their Pokémon within the Boxes, but is not necessary for game
> play. Each Pokémon can be marked with any combination of the different
> markings. Prior to Pokémon Black 2 and White 2, this could be done
> only while the player was operating the Pokémon Storage System. In
> Generation III, there were four markings: ●, ■, ▲, and ♥. In
> Generation IV, two more markings were introduced and the existing ones
> were reordered, making the full list ●, ▲, ■, ♥, ★, and ♦, in that
> order (this order is kept in all later generations). The markings
> appear in the Pokémon Storage System and on the Pokémon's summary
> screen. A Pokémon will keep its marking settings if traded to another
> Trainer.

Taken word for word from here. TL; DR: Markings don't do much bar making organizing easier. I know that many people use the symbols to denote 31 IV stats on bred Pokemon, to mark out the best for competitive.

Answer 2

They are used to mark the Pokemon stats .

There are coincidentally 6 marks (equal to the number of stats: HP, Atk, Def, Sp.Atk, Sp.Def, Spd) you can 'mark' or un-'mark', which can be ideal to mark what stats of a Pokemon are at 31 IVs, which I've found to be the most common use of these.

Of course, it's entirely up to you to decide what to do with them.

You can 'mark' or un-'mark' from the summary page of a Pokemon or through the 'Marking' option in your PC box.

Eg:If you have 2 ditto 1 with fully EV trained on certain stat and other 1 is not.So you can mark the ditto with fully EV trained stat.

.Source