You have a truly beautiful Signature Block!
The tiny white line is a combination of a darker background with the contrasting white on Murphy, which highlight the tiny white line.
The development of the technology that drives this and other Forums was developed before HD, High Res screens that highlight near everything. The end result is items like this that are forced because of HD, High Res technology.
There are choices in this World, and Free Web is one of those choices. You are viewing this and many other Forums and Sites as no cost to you! For that to keep happening, advertising is common, but not overly intrusive.
To correct tiny issues like this would require all new technology and its operating software. That would require either a great increase in, which would include intrusive advertising and/or paid access viewing.
Personally, I'm willing to accept the tiny white line.