[AndySedeyn]

You can do two things:

• Keep count on how many objects the player already has:
  
  PHP код:

  enum E_PLAYER_DATA {

    tagCount
};
new PlayerInfo[MAX_PLAYERS][E_PLAYER_DATA];

enum E_TAG_DATA {

    // enumerators
};
new TagInfo[MAX_PLAYERS][MAX_TAGS_PER_PLAYER][E_TAG_DATA];

CMD:create(playerid, params[]) 
{ 
    if(PlayerInfo[playerid][tagCount] >= MAX_TAGS_PER_PLAYER)
        return SendClientMessage(playerid, -1, "You have reached the maximum amount of tags per player.");
    
    new tagIndex = ((PlayerInfo[playerid][tagCount] == 0) ? (PlayerInfo[playerid][tagCount]) : (PlayerInfo[playerid][tagCount] - 1));
    TagInfo[playerid][tagIndex][TagObject] = CreateDynamicObject(19482, X, Y, Z, 0.0, 0.0, 0.0, -1, -1, -1, 300.0, 300.0);
    return 1; 
} 

• Or via more sophisticated loops:
  
  PHP код:

  enum E_TAG_INFO {

    bool:tagExists
};
new TagInfo[MAX_PLAYERS][MAX_TAGS_PER_PLAYER][E_TAG_INFO];

function SprayTag_GetFreeID(playerid) {

    for(new i = 0; i < MAX_TAGS_PER_PLAYER; i++) if(!TagInfo[playerid][i][tagExists]) {

        return i; // Return the free index
    }
    return -1; // All tags are in use (= player has reached MAX_TAGS_PER_PLAYER tags).
}

CMD:create(playerid, params[]) 
{ 
    new tagIndex = SprayTag_GetFreeID(playerid);

    if(tagIndex == -1) {

        return SendClientMessage(playerid, -1, "You have reached the maximum amount of tags per player.");
    }

    TagInfo[playerid][tagIndex][TagObject] = CreateDynamicObject(19482, X, Y, Z, 0.0, 0.0, 0.0, -1, -1, -1, 300.0, 300.0);
    return 1; 
} 


These are just short and incomplete examples on how you could tackle the problem.