here is great example of the line which should not be used as a trading signal. lets make it an exercise - the question is why it is not good. i hope you all remember theory - you will find answer there (itrademyself.com)
2009 October +533
2009 November +1493
2009 December +1260
2010 January +3390
2010 February +2414
2010 March +689
2010 April +1009
2010 May +867
2010 June +407