Steemit, like many websites, uses a symbol after links which go to outside websites. It's a square with an arrow coming out of it. But that symbol isn't text. In fact, in Steemit's implementation it's a Scalable Vector Graphics (SVG) image embedded right in the site's style (its CSS).
<svg height="1024" width="768"
xmlns="http://www.w3.org/2000/svg">
<path d="M640 768H128V257.90599999999995L256
256V128H0v768h768V576H640V768zM384
128l128 128L320 448l128 128 192-192
128 128V128H384z"/>svg>
(That CSS looks like it may have been generated by something with a floating point rounding problem... I wasn't able to find it in the condenser source code, but it's gotta be there somewhere: https://github.com/steemit/condenser)
So why isn't there a Unicode character for this commonly-used symbol?
The Unicode Graveyard
The "Archive of Notices of Non-Approval" lists all the proposals made to the Unicode Consortium which have been formally rejected, and would prefer not to see again. There was specific proposal to add EXTERNAL LINK SIGN to Unicode, which you can read here: https://www.unicode.org/L2/L2006/06268-ext-link.pdf The rationale given there:
The UTC rejected the proposals to add "external link sign", most recently in L2/12-169. It is unclear that the entity in question is actually an element of plain text, given the inevitable connection to its function in linking to other documents, and thus its coexistence with markup for links. Furthermore, the existing widespread practice of representing this sign on web pages using images (often specified via CSS styles) would be unlikely to benefit from attempting to encode a character for this image. (This notice of non-approval should not be construed as precluding alternate proposals which might propose encoding a simple shape-based symbol or symbols similar in appearance to the images used for external link signs, should an appropriate plain-text argument for the need to encode such a simple graphic symbol be forthcoming.)
Unicode wants to limit itself to "text". It has decided that a marker appearing in text, and text only, is somehow not text. Admittedly, when copying and pasting one probably doesn't want to include the external link marker. But that's different from claiming that it's not as valid a punctuation character as ?, ., or !. The symbol is far more tightly coupled to text and textual displays than something like ✈ (U+2708, AIRPLANE) which I've only seen on road signs.
It's especially galling for Unicode to make this argument, while approving new emoji all the time (how are they plain-text?) and including such "legacy" code blocks as Box Drawing. Who knows what uses writers would find, should an external link character be readily available to them?
(Quora Q&A that sparked this rant: https://www.quora.com/What-are-the-reasons-Unicode-gives-for-rejecting-certain-characters-or-writing-systems/answer/Adrian-Ho-2)