Take the pokemon to the lady who hands out the Effort Ribbons in that little market place in Slateport. If your pokemon has reached the max amount of EVs, they'll get a ribbon.
Or, what I do while EV training is I make tally marks for every EV my pokemon gain on a little notepad. I write down the stat I'm building and just keep tallying up the EVs and then count them up frequently to see how much they've gained. That's the easiest way.
Although when tallying EVs, instead of the normal four ticks and then diagnal slash to count five, you only need to tally four at a time. 4 Evs= 1 stat point. So make three tick marks, and then dash them on the fourth one.