What are ForEx signals?

A ForEx signal is not an indication of anything, it is a recommendation for which the signal provider hold no responsibility for whatsoever. In other words, if you follow a signal you have surrendered your own decision making to someone who may very well profit if you lose. 

Many signals are machine generated and so are only basing decisions on micro changes in prices that usually bounce back or indicate the beginning of a trend. They may well be profitable most of the time, but with the nature of ForEx, spread betting and CFDs, one bad decision is all you need to lose everything.

Some signals come from seasoned traders but you have to bear in mind that a really good trader isn't going to want to sell their information on as it could corrupt their outcomes and create new trends. In most circumstances, those who can do, and those who can't pretend to and/or teach.

As well as signals there are also various algorithms that can be bolted onto your MT4 or MT5 system that can help with the majority of situations. As with signals though, choosing the wrong provider can accelerate failure rather than profit.

Both of the above practices are similar in concept to copy trading which is essentially reusing a strategy that has been or is being created by someone else. You can essentially mirror a traders activities on your system or copy another traders actions from a similar market condition. Once again this means you are surrendering some or all of your control to another conviction which may not be a good option.

In general, any of the above services that are supplied for free are a bad idea. If you are paying for signals or trading advice or mirroring in some way then you at least have some come back as long as the advice comes from within your territory or country.