Hint: "People and dates with lasting effect."
The initials on the mural correspond to the names of the inventors, most of whose whose inventions depicted:
- EW = Eli Whitney invented the cotton gin 1794
- HD = Humphrey Davy - Demonstrated electric lamp to the Royal Society - 1806
- JW = John Whitehurst - Pulsation Engine (hydraulic pump) - 1722 other possible answer James Watt - Improved steam engine - 1763
- BF = Benjamin Franklin - Pointed light rod conductor - 1752
- GLL = George Louis Lesage - Used a single wire system to telegraph a message - 1774
- LP = Louis pasteur - Process of sterilizing milk - 1862
- GS - George Stephenson - Locomotive - 1814
- GM = Guglielmo Marconi - Radio - 1901
*AGB = Alexander Graham Bell - Phonophone (or more commonly, the telephone) - 1880
- CM = Cyrus McCormick - Inventor the Reaper - 1809
- TE = Thomas Edison - Invented phonograph - 1877
The San Francisco picture  shows 3 items above the same starburst(?) pattern: A locomotive (invented by George Stevenson/GS), a telephone (invented by Alexander Graham Bell/AGB); both represented in the mural. The only one not represented is the statue of Poseidon, whose son is TRITON. ((Great! What does that have to do with the puzzle?))
The puzzle clearly indicates that dates are somehow significant "PEOPLE AND DATES WITH LASTING EFFECT". The complication I ran into were that dates attributed to the inventions shown are very sketchy in many cases. When I decided to take the first date associated with the invention or underlying principle behind each item I came up with this (quotes taken from web references found with Google):
Eli Whitney - cotton gin - 1793 - "Whitney produced the first crude model of his gin in 1793"
Humphrey Davy - electric lamp - 1801 - "In 1801 Sir Humphry Davy, an English chemist, made platinum strips glow by passing an electric current through them"
James Watt - steam engine - 1764 - "Watt’s work with the steam engine began in 1764, when he was requested to repair a Newcomen steam engine used at the university."
Benjamin Franklin - lightning rod - 1747 - "In 1747 Franklin began his experiments in electricity with a simple apparatus that he received from a friend in England."
George Louis Lesage - telegraph - 1774 - "The first telegraph was demonstrated in Geneva, Switzerland in 1774 by George Louis Lesage."
Louis Pasteur - pasteurized milk - 1856 - ".. in 1856 .. Pasteur’s experiments on bacteria began, resulting in the process that still bears his name (pasteurization)."
George Stephenson - locomotive - 1814 - "Stephenson designed his first locomotive in 1814"
Guglielmo Marconi - radio - 1895 - "late in the summer of 1895, Guglielmo Marconi made the first tentative wireless transmissions"
Alexander Graham Bell - telephone - 1876 - "until 1876, when Alexander Graham Bell placed the first phone call."
Cyrus McCormick - reaper - 1831 - "By the end of the same 1831 harvest, Cyrus had the first successful demonstration of his reaper."
Thomas Edison - phonograph - 1877 - "August 12, 1877, is the date popularly given for Thomas Alva Edison's completion of the model for the first phonograph,"
I'll be the first to say that the date attributed to Benjamin Franklin seems to be a stretch given that the picture appears to be a lightning rod which he did not invent for many more years.
Now, taking the last digit of each year as an index into the inventors name we get:
I HEIR PRINCE
Triton could indeed be called the heir prince of Poseidon (depicted in the 3rd image with the matching key symbol from this puzzle).
The accepted answer is: triton
Next book: Tomb