Code:

$ strings -n 20 ~/.primecoin/blocks/blk00000.dat
[...]
"All hail king sunny"
"All hail king sunny"
=This block was mined with mtrlt's GPU miner version 0.01 Beta
!100% Naturally Grown Prime Chains
=This block was mined with mtrlt's GPU miner version 0.01 Beta
=This block was mined with mtrlt's GPU miner version 0.01 Beta
=This block was mined with mtrlt's GPU miner version 0.01 Beta
=This block was mined with mtrlt's GPU miner version 0.01 Beta
=This block was mined with mtrlt's GPU miner version 0.01 Beta
=This block was mined with mtrlt's GPU miner version 0.01 Beta
)=This block was mined with mtrlt's GPU miner version 0.01 Beta
1=This block was mined with mtrlt's GPU miner version 0.01 Beta
=This block was mined with mtrlt's GPU miner version 0.01 Beta
=This block was mined with mtrlt's GPU miner version 0.01 Beta
=This block was mined with mtrlt's GPU miner version 0.01 Beta
=This block was mined with mtrlt's GPU miner version 0.01 Beta
.=This block was mined with mtrlt's GPU miner version 0.01 Beta

The first block was there already last week, the others were added between end of last week and now. I guess that's mtrlt testing, because if this is truly the only blocks mined with his GPU miner, it's nothing. People should stop shouting scammer all the time in these forums. Development is not always straight-forward, and some people have a live as well.