[Shabi RoxX]

Here's a rough idea:

pawn Код:

new Text3D:dmtext;
new PlayerInDM;
//create dmtext at OnGameModeInit()
OnGameModeInit()
{
//other codes
dmtext = Create3DTextLabel("Player: 0",color,X,Y,Z,DD,VW,0);// change x,y,z,dd,vw to your 
}
if(strcmp("dm",cmd,true) == 0)
{
new str[12];
PlayerInDM++;//increasing players count on each /dm cmd
format(str,sizeof(str),"Players: %d",PlayerInDM);
Update3DTextLabelText(dmtext,color,str);
}

Note: Wrote it here , never tested it, just check spells or syntex