LIGPLOT symbols:-

Ligand bonds are shown with thick lines (here in purple).
Non-ligand bonds (ie belonging to those protein residues to which the ligand is hydrogen-bonded) are shown with thin (orange) bonds.
Hydrogen bonds are shown by dashed (green) lines with the length of the bond printed in the middle.
Hydrophobic contacts between protein and ligand are indicated by the (brick-red) spoked arcs. Protein residues involved only in these contacts with the ligand are shown by a single spoked arc. Other atoms involved in hydrophobic contacts have spokes coming out of the individual atoms.
Atomic accessibilities are (optionally) shown by shaded circles around the atoms. The thicker and darker the circle, the more buried and solvent inaccessible the atom. Exposed, highly accessible surface atoms are surrounded by a thinner, lighter circle.
Chain identifiers (where relevant) are shown in parentheses after the residue names.

Note that the parameter file, ligplot.prm, allows you to alter these symbols in terms of:-