The string "<!--MKS HTML-->" is inserted by Integrity to tag the contents of rich text fields (of type long text).
But fields with logging capability are not rich text so they display the tag if the value originally came from a rich text.
If you simply copy/paste from a rich text to a logging field, the output is usually right. If you convert a rich text field to logging I think you'll see the tags.
If you're simply converting field types as you develop the system, don't worry about removing the tags. If not and you want to clean up logged data, you have to convert the field back to not logging and not rich text, fix the contents, then switch back to logging. Usually not worth the effort.
It's hard to understand from the picture the whole sequence of what you did. Did you just paste the contents from a rich text field into this one and you haven't saved yet? There's no logging history showing.
The field you highlighted looks like rich text (inside a table cell). So is it really logging?
Please provide more details.
I suggest you change the title of your question to "How to get rid of <!--MKS HTML-->" so it can be found in future searches. "Highlighted text" refers to your picture which doesn't display in emails or searches.