Is there a character equivalent to the underscore " _ " which occupies the upper position? Dash " - " will not do. If it were me, I would call it upper-score. But I do not see this anywhere.
What you seek is generally known as a "macron", "overline", "overscore", or "overbar". It exists at several Unicode code points; which one you want depends on whether you want a macron or an overline (the former being shorter), and whether or not you want a combining character.
From Wikipedia, an overline may be found at U+203E (spacing) or U+0305 (combining), and a macron at U+00AF or U+02C9 (spacing, and apparently identical in appearance), or U+0304 (combining).
You could try a web service to look up the unicode character you want by drawing.
Horizontal scan line-3: ⎻
Unicode hexadecimal: 0x23bb
Combining double macron: ͞
Unicode hexadecimal: 0x35e
Upper one eighth block: ▔
Unicode hexadecimal: 0x2594
Combining overline: ̅
Unicode hexadecimal: 0x305