The Arduino signals are sometimes called "logic" signals or "TTL-level" signals.
The Arduino RX and TX are idle high. The start-bit is low, then the data bits, low = 0 and high = 1, then the stop bit which is high. That is non-inverted.
The RS-232 is inverted.
Some devices use inverted TTL-level UART. That is not normal, but there is no real standard.