The Sheshawnii, as a society, have very few common taboos. Any others are often personal choice, such as someone touching a Dawncry's journal without permission.
Scalping is the most offensive and worst way to kill a Sheshawnii. By scalping (i.e., destroying their body to the utmost decree and permanently removing their soul), it destroys the Balance that fills the Sheshawnii Lands. Under such an occurance, if a native of Sheshawnii is scalped, their body's energy is returned to the earth, permanently ending their life cycle, and stopping them from being able to properly be reborn. Those who break the scalping taboo are often punished, as this is treated as a high crime, rather violently. The offender is banished, or more commonly, treated to the same fate.
For this same reason, eating meat is view in poor taste, and will never happen in a formal setting. While it is commonly practiced, the reason for this taboo is the knowledge that everything known comes from the land, and upon death, you return to the land. By eating meat, you run the risk of possibly eating reincarnated friends and family.