Custom Depreciation Method Name Restrictions

Are there restrictions on the method name?

The following two-character codes are reserved by the system. Therefore, you cannot enter the following codes in the Enter New Name and Description field:

aa	de	ma	oc	sh
ad	dh	mf	rv	sl
at	di	mi	sa	st
db	dl	mr	sb	yd
dc	dm	mt	sd	yh
dd	dy	no	sf	ys