-----BEGIN BITCOIN SIGNED MESSAGE-----
Date: 10/05/2021
This is the real owner of the bitcointalk account :Martin958
My bitcointalk profile is:
https://bitcointalk.org/index.php?action=profile;u=314728-----BEGIN SIGNATURE-----
bc1q5x06na8urh3f9sx6j8d9js00zrltsn4uzp5r6r
H2c46zCwwE0ujWlCuA5k0TKZcOCdGpq8TAiEEpJVykXKWVmBD+g1F057ONiogY0KRTgW9JCqpULvwq11uOHdPQg=
-----END BITCOIN SIGNED MESSAGE-----
Maybe there is some space or double quote that you have lost by mistake? Which wallet are you using for signing this message?