Thwarting spammers on hashtag livetweeted events

Summary
Type this into Twitter's search page (or on your smartphone Twitter app's search)

#hashtag -x.co

where #hashtag is the tag you're interested in and x.co is the URL shortener being used by spammers (eg it could be -bit.ly).

Note that this also works on Storify should you want to capture the hashtagged tweets minus the spammers' contributions.

Update 21 Jan 2014 (welcome #iscg visitors) - you can also use the slightly more obscure URL shortener is.gd to shorten your URLs, chances are the spammers restrict themselves to x.co and bit.ly. There are a variety of URL shorteners out there so it's possible to keep a step ahead. Good luck and happy conferencing :)

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More detailed explanation
We all know that if a word, phrase or hashtag starts trending then it attracts the interest of spammers hoping to exploit the eyeballs of those watching the stream of tagged tweets.

Generally spammers include a link, though sometimes it's just text (rarer) and if they do then it's worth trying to subtract the root URL from the hashtag search.

So if you're watching the search output results from #RCGPSoMe (Royal College of General Practitioners Social Media chat) and annoyed by spam links coming from x.co then search for #RCGPSoMe and not for x.co, thus:  #RCGPSoMe -x.co which gives you this URL:

https://twitter.com/search?q=%23RCGPSoMe%20-x.co&src=typd

(the %23 means # and %20 is just a space).

Since the spammers are also using bit.ly then I'd recommend pruning that one out too, so type into Search
#RCGPSoMe -x.co -bit.ly and remind people to use tinyurl.com or t.co or some other URL shortener so their tweets aren't mangled too.

Search for #RCGPSoMe -x.co -bit.ly which gives you 

https://twitter.com/search?q=%23RCGPSoMe%20-x.co%20-bit.ly&src=typd

1. This works both on https://twitter.com/search (ie the web version) and on Echofon on my iPhone, just by typing in the keystring
2. I'm aware there's an app / tool / site which will collect tweets only from people who've registered, ignoring the spam, but have forgotten what it is. Tweetchat.com will help a bit but not perfect.
3. The search string also works on Storify! This means you can semi-automate the capture of appropriately hashtagged tweets, hooray.

I can't take credit for the search string though it was certainly a case of fortune favouring the prepared mind. I suspected it might work and Googled to see if others had investigated and these two had come up with something: A trick for stopping event hashtag spam (1 October 2012) but an alternative, which may not work as well now that Twitter has hidden the info on the app used to send the tweet, was Finding ways to battle hashtag spam (7 May 2012).