It appears it stops displaying at 99, there are currently 360 questions with a bounty on Stack Overflow and when the URL is changed to point at SO it displays like this:
PeterJ is correct, the counter stops at 99 because the number of digits is fixed at exactly two. I recommend against using this community ad on large sites that routinely have more than 99 active bounties as it obviously won't be showing the correct number during those times.
In this particular case, as animunson pointed out in a comment, content in Pastebin pastes is licensed under CC-BY-SA 3.0, the same license that Stack Exchange posts are covered by. So from a legal perspective, you already have the author's permission to copy any amount of the content into an answer here.
But suppose you had asked about something which you ...
Why wouldn't it be? If you've found more information, or an authoritative source, or someone else's experiments with the problem at hand, or whatever-else-relevant, include it! Stack Overflow is designed to be a repository of useful knowledge; including more useful knowledge is good.
One caveat: don't just link to the other resources. Quote them, interpret ...
From an answer on MSO by George Stocker, this is some good guidance for writing an answer that recommends an external resource (emphasis mine):
A good answer that involves an off-site resource references the
What is this thing you're talking about?
Where do I install it?
How do I install it?
How do I use this thing to solve the ...
If your only goal is to post the link, then as Shadow Wizard has answered, you can use an ad or your profile. But if you just wish that everyone knew how to X, and you've written a tutorial about it, then you can take the advice in How can I link to an external resource in a community-friendly way?
You come across (or search for and find) a question (...
Each Stack Exchange site got something known as Community Promotion Ads.
Those are advertisements that are published by the users themselves, in the per-site meta.
For example, for Physics.SE the current meta post with the ads is: Community Promotion Ads - 2017. (To find it on any site, go to its meta and browse the community-ads tag.)
In there anyone can ...
If you find a useful resource, provide a link to it - that's ok as long as you first explain the solution within the SE answer box. Your answer has to stand on its own even without a link. A link can just support it.
If a quote provides a great explanation, include it, properly attributing it. There's no need to come up with your own words if someone did ...
Referencing external sources is absolutely fine, and encouraged, but you should really be quoting the important parts and explaining in your own words how it answers the question at hand.
How much you quote and how much you explain in your own words is really up to you. Posting an answer that consists entirely of external material doesn't sit well with me. ...