I'm afraid this question might be too localized, but I have no better place to ask it:
In the section Classes which interpret any structure of his Model Theory Hodges shows how each $L$-structure $B$ can be converted into a graph $A = \Delta(B)$, $L$ a first order language with finite signature.
He associates every element of $B$ with a so-called 5-tagged element $a$ of $A$. Likewise he associates the i-th symbol of the signature $S_i$ with a (i+6)-tagged element of $A$. For further details see Hodges, p. 228 ff.
The only question I have at this point is: Why isn't it enough to associate all the relation symbols with different 6-tagged (and 6-tagged only) elements of $A$? Why is it necessary - for his argument's sake - to distinguish them further by their "tag count"?