This class labels subplots or tiles in a composite figure. Say, you are having several subplots like this on here:

for r = 1:6; subplot(2,3,r); plot(rand(5)); end

Now, you can create the plot as shown in the figure by following command:

h = subplotlabel(gcf,'a','location','southwest');

subplotlabel makes it easy to change the size of the labels using the commands
bigger(h) or smaller(h), or the font style with italic(h) or bold(h)