I don't know whereabouts 'Pb' comes from in the greater branding arcana but schoolboy memories suggest that it has something to do with lead - as in nicking church roofs.
You look through this extremely neat site and you are suddenly aware that chemical abbreviations are used all over the place as logo-ettes reinforcing links to other pages. So that Li (lithium but also possibly Roman for 51 or Chinese for circa half a kilometre) is found next to the 'LInks' box. Oh, there in very small type is 'Lithium' and above that its mass per cubic centimetre and another number which I thought might be its number on the periodic table but wasn't.
Hold on. What's all this about? And how long did it take to work out that Au, the chemical abbreviation for gold could be used with the About Us link to the usual Death Row mugshots? The 21 Caret Gold team! High fives all over the office when somebody got that.
I don't want to be scathing about needing to find things to do during the long, dark winter up there in the Northwest. But this is the sort of conceit, feuillage, decoration which otherwise useful link headings on a website just don't need. Remember Adolf Loos: Ornament is crime.