When 2 letters overlap or connect, either deliberately or coincidentally so that they appear as a single unit, they form a ligature (a word that means that they are tied or bound together).  Of the 21 LMLK seals, ligatures appear on 4 of them:  the H4C "BR", S2U "KE", S4L "SU", & M2T "MM".

                 

The S2DW & S2DR almost have "SU" ligatures like the S4L, which is interesting since you'll notice that these 4 ligatures represent 4 of the 5 LMLK seal sets--all except for the x2D. Also note that the H4C "BR" ligature appears in lines 1 & 5 of the Siloam Inscription from Hezekiah's tunnel (enclosed by yellow circles in this drawing):

Drawing adapted from Kata-Pi Bible Resource Pages; photo from "The Ancient Near East in Pictures Relating to the Old Testament (2nd ed. w/ supplement)" by James B. Pritchard

This spectacular color photo is a close-up of the actual BR ligature in the 5th line, taken by Todd Bolen of BiblePlaces Dotcom while visiting the Istanbul Archaeological Museum: