It's pretty in character for Senku, who seems to have a thing for Einstein. Later on when cameras are made and his photo is taken
, he sticks his tongue out to mimic Einstein.
E=mc^2 is probably the world's most famous equation. It's also really simple and easy to explain, but the amount of science needed to discover it is staggering. Let alone employ its applications. Rebuilding society and technology to the point of splitting the atom is a monumental task. Every day when he puts on his imitation labcoat, it's a reminder to Senku of what the world once had and what he's aiming for. And should he fail and die alone and someone comes across his corpse, they'll have an idea of who he was and what he was trying to accomplish.
To be honest, Einstein would probably be proud to have his equation used like that rather as the inspiration for nuclear weapons. While he did sign the letter urging US development of nuclear weapons at the time, he later regretted his decision.
Senku writing it in blood was just fucking stupid though. He didn't make soap until half a year later, so he was just asking to get infected.