Why do you think Fives never put anything on his armor to honor Echo? Was it because it hurt too much and it cemented the fact he was gone?
It’s the environment they are made to become accustomed to.
When they are young, first starting out, the pain is fresh. Friends die. They try to do what they can to remember them. They make ceremony, they do homage. But then more friends die. And more. And even more.
There is not enough space on their armor. Not enough skin to bear the ink.
Eventually, their pain and mourning is tinged with other things: anger, frustration, exhaustion.
And despite that constant – almost to the point of routine – loss, they are made to move forward. To go back into the fray and fight.
Once they are fighting, they cannot carry the burden of their loss too tightly. They can’t afford to be distracted.
However, despite all this, I think there are also other ways to commemorate the loss of a loved one that goes beyond bearing marks and paint. Sometimes it can be actions, oaths, small hidden tokens.
So, even if there is nothing that we see immediately that visually marks something to honor Echo, I don’t doubt that he still honored him in another way.