Show an object once when another object appears on the screen

There is an horse icon which is moving left to right in every 15 seconds and when that icon appears on the screen, another sprite(Collect Horse) will show up and it will disappears after 2 seconds. So, the problem is, the sprite(Collect Horse) is showing time to time when the horse icon appears on the screen. I want it to show only once when the game starts.

As well as the condition 'horse icon is on screen', add a global variable condition like variable=true, then on the action where you show the other sprite set the variable to false, this will lock out the event.