Since upgrading the Discord Extension and Rustcord I've been seeing this error when some uses sign artist and it gets logged to a discord channel. Everything appears to still be working. But this error comes up in the console. 

[Discord Extension] [Error]: Discord API has returned error Discord Code: 50035 Discord Error: Invalid Form Body Request: [POST] https://discord.com/api/v9/channels/757995303151599627/messages (Response Code: BadRequest)
Discord Errors: {
"embeds": {
"0": {
"image": {
"url": {
"_errors": [
{
"code": "URL_TYPE_INVALID_SCHEME",
"message": "Scheme \"v\" is not supported. Scheme must be one of ('http', 'https')."
}
]
}
}
}
}
}
Request Body:
{"embeds":[{"title":"BuZZBoy posted an image to a sign.\nPosition: (-801.3641 18.71163 697.3607)","color":52326,"image":{"url":"v"}}]}

I guess your error happens because the player (or you) try to use the wrong image link?

I had the same error for DiscordStatus when type ?players command in discord and then found that guy had his server.headerimage set to 1 lol... how is this 1 is actual server banner image link? Because discord Status fetch this link to display the banner as thumbnail in the embed was going boom like this until added proper link for headerimage.

I guess your issue is the same. Just do /sil ProperLinkEndingWith.png/.jpg and should works on in-game sign + log to discord...
If players who tried this typed /sil v I guess he was either misstyping command or tried /sil CTRL +V to paste link but instead only typed V and hit enter... 

I see this is old topic but because got the same issue now and found no help, decided to answer here for you and probably other people in the future...