Possible Clues:

• Literary monogram
• "Nature" author's monogram
• "Self-Reliance" essayist's monogram
• Monogram of the literary figure who was the landowner of the residence at 39 Across
• 'Nature' essayist's inits
• Inits. of Thoreau's mentor
• "The American Scholar" essayist's monogram
• 'Self-Reliance' essayist's inits
• The Concord Sage's monogram
• Monogram of 'the Sage of Concord'