I looked up the D3300 instructions, and wow, they're worse than ever! There isn't even an index now.
As far as I know, this icon does not appear on a D3200, but it looks as if this is the new indicator for potential camera shake when the shutter speed is slow. On the D3200 it flashes the aperture, and the question mark when exposure is out of range, but has no specific icon for slow shutter speed.
You can probably experiment with this by setting the camera to shutter priority mode, and turning the shutter speed up. If the symbol goes away above 1/30 second or so, that's it.
Edit to add: That icon is common and long standing on some other brands such as Fuji, but seems to be new to Nikon. I often suspect that the people who write the manuals have not actually spent much time with the camera. Someone develops the camera and hands it to them and says "figure it out."
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As far as I know, this icon does not appear on a D3200, but it looks as if this is the new indicator for potential camera shake when the shutter speed is slow. On the D3200 it flashes the aperture, and the question mark when exposure is out of range, but has no specific icon for slow shutter speed.
You can probably experiment with this by setting the camera to shutter priority mode, and turning the shutter speed up. If the symbol goes away above 1/30 second or so, that's it.
Edit to add: That icon is common and long standing on some other brands such as Fuji, but seems to be new to Nikon. I often suspect that the people who write the manuals have not actually spent much time with the camera. Someone develops the camera and hands it to them and says "figure it out."