Where this device is formed from a capital, it’s called a swash and there are many font variants with “Swash Capitals”. Originally it was designed to fill the space between letters1, but often now swash capitals incorporate strokes which are far more ornate or elongated than a simple space filler.
In the absence of anything better, the term might easily be applied to the stroke in the illustration.
1 OED, 1918: Printing. Applied to old-style capital letters having flourished strokes designed to fill up unsightly gaps between adjacent letters.
Source : Link , Question Author : David Starkey , Answer Author : Andrew Leach