What is component 3 in figure T-1?

The schematic symbol for an indicator lamp or incandescent light bulb is typically drawn as a circle enclosing a stylized filament. This interior graphic often looks like a small loop, a bump, or sometimes an 'X'. This symbol directly represents the physical structure of a classic light bulb, where a thin wire filament glows brightly when electrical current passes through it. Distractors like ground symbols (decreasing parallel horizontal lines) or transistors (three-leaded circles) look completely different.