A non-Jew is forbidden from observing Shabbos. When someone is in the process of converting, we advise them to keep the entire Shabbos besides for doing one forbidden activity. A common practice is to carry something in their pocket (if there is no eiruv). However, according to some carrying is generally only breaking Shabbos on a Rabbinic level since most city streets have only the status of a karmalis (rabbinic public domain), not a reshus harabim (biblical public domain). Is it sufficient to break Shabbos on a Rabbinic level to avert the problem of a gentile keeping Shabbos? Woudn't it be better to tell them to switch on an incandescent light bulb in their room, or some other action which is simple to do and violates Shabbos on a biblical level according to everyone?