title: How can I include custom point symbols in legend
body: <p>Consider the following data / plot, which works as I am only assigning numeric values to <code>pch</code>.</p>
  
  <pre><code>plot(1:20, col='blue', pch=20); 
  points(2:22, col='red', pch='+', cex=2)
  points(4:24, col='green', pch=15)
  
  legend('bottomright',c('Blue','Red', 'Green'),   
         col=c("blue", "red", "green"), horiz=T, cex=0.8,
         pch=c(20,20,15), bg='white')
  </code></pre>
  
  <p>But when I include a character value, it still plots a legend, but uses the <strong>wrong point types</strong>.</p>
  
  <pre><code>legend('bottom',c('Blue','Red', 'Green'),   
         col=c("blue", "red", "green"), horiz=F, cex=0.8,
         pch=c(20,'+',20), bg='white')
  </code></pre>
  
  <p>And when using only character values, the legend is correct again:</p>
  
  <pre><code>legend('bottomleft',c('Blue','Red', 'Green'),   
         col=c("blue", "red", "green"), horiz=F, cex=0.8,
         pch=c('!','+','*'), bg='white')
  </code></pre>
  
  <p>The legend in the middle is the problem. <em>How can I plot the legend with correct point types?</em></p>
  
  <p>I know that i could use <code>pch=3</code> for a "+" symbol, but what if i'm trying to plot a "!" symbol instead?
  <a href="https://i.stack.imgur.com/ggI9t.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/ggI9t.png" alt="plot"></a></p>