You have copied wrong link. Direct image link from
imgur will not work on forum. There is different link with bb code, you should copy directly and just paste it. You can follow below screenshoot. If you are in mobile then use desktop version.
Your code should look like below. You need just copy paste. Don't add anything more.
[img]https://i.imgur.com/3cqG45L.jpg[/img]
Try it now by yourself or try with copy paste my code.
You can try also
https://imgbb.com Edit :
Where i can learn to make bitcoin signature code .If you know means kindly share that link or video .
Here is BB code tutorial:
https://bitcointalk.org/index.php?topic=1727100.0Note; please use search button before you ask question or make new thread. Thanks.