There are many ways to share a link with someone: Twitter, Facebook, IM, email and more.
But if your friend is close by then you could just broadcast it via specially encoded audio tones.
Chirp, a free app for Android and iOS, has been doing this for a while. In a click or two it can encode a URL, text note, maybe an image, then play it as a series of tones. Sounds bizarre, but it can work well -- depending on background noise -- and others can access your data without needing account names, addresses or anything else.
Recently Chirp added a Chrome extension to its arsenal. This can only broadcast links right now -- it can’t receive anything -- but does give you another way to send information from a desktop to an iOS or Android device.
Just to demonstrate that this isn't quite as bizarre as you might think, even Google has now entered the fray with its own version of the technology.
Google Tone is another Chrome extension, basic but extremely easy to use. When you're at a link you'd like to share, simply click Google Tone's address bar button, and it plays the link as a series of tones. Any other users in earshot should get a notification saying you’re sending them a link, and if they’re interested, clicking it will open the page in a new tab.
If you're interested in the idea, start with Google Tone. It has some drawbacks -- you can only share page URLs, you must be logged in with a Google account -- but it's straightforward to use, and you'll quickly see if the technology might work for you.
Then, if you need more power, take a look at the Chirp app, where you can broadcast pictures, MP3s, documents and more. How well it's going to work depends very much on your devices and environment, but we saw good results, and a four star rating at the App Store suggests others are happy, too.