Source: Noto Sans Symbols 2

U+2621 Caution Sign

U+2621 was added in Unicode version 1.1 in 1993. It belongs to the block U+2600 to U+26FF Miscellaneous Symbols in the U+0000 to U+FFFF Basic Multilingual Plane.

This character is a Other Symbol and is commonly used, that is, in no specific script.

The glyph is not a composition. It has no designated width in East Asian texts. In bidirectional text it acts as Other Neutral. When changing direction it is not mirrored. The word that U+2621 forms with similar adjacent characters prevents a line break inside it.

The Wikipedia has the following information about this codepoint:

The dangerous bend or caution symbol ☡ (U+2621 ☡ CAUTION SIGN) was created by the Nicolas Bourbaki group of mathematicians and appears in the margins of mathematics books written by the group. It resembles a road sign that indicates a "dangerous bend" in the road ahead, and is used to mark passages tricky on a first reading or with an especially difficult argument.

Representations

System	Representation
Nº	9761
UTF-8	E2 98 A1
UTF-16	26 21
UTF-32	00 00 26 21
URL-Quoted	%E2%98%A1
HTML hex reference	☡
Wrong windows-1252 Mojibake	â˜¡
Encoding: GB18030 (hex bytes)	81 37 A5 37

Elsewhere

Complete Record

Property	Value
Age (age)	1.1 (1993)
Unicode Name (na)	CAUTION SIGN
Unicode 1 Name (na1)	—
Block (blk)	Miscellaneous Symbols and Pictographs
General Category (gc)	Other Symbol
Script (sc)	Common
Bidirectional Category (bc)	Other Neutral
Combining Class (ccc)	Not Reordered
Decomposition Type (dt)	none
Decomposition Mapping (dm)	Caution Sign
Lowercase (Lower)	✘
Simple Lowercase Mapping (slc)	Caution Sign
Lowercase Mapping (lc)	Caution Sign
Uppercase (Upper)	✘
Simple Uppercase Mapping (suc)	Caution Sign
Uppercase Mapping (uc)	Caution Sign
Simple Titlecase Mapping (stc)	Caution Sign
Titlecase Mapping (tc)	Caution Sign
Case Folding (cf)	Caution Sign
ASCII Hex Digit (AHex)	✘
Alphabetic (Alpha)	✘
Bidi Control (Bidi_C)	✘
Bidi Mirrored (Bidi_M)	✘
Composition Exclusion (CE)	✘
Case Ignorable (CI)	✘
Changes When Casefolded (CWCF)	✘
Changes When Casemapped (CWCM)	✘
Changes When NFKC Casefolded (CWKCF)	✘
Changes When Lowercased (CWL)	✘
Changes When Titlecased (CWT)	✘
Changes When Uppercased (CWU)	✘
Cased (Cased)	✘
Full Composition Exclusion (Comp_Ex)	✘
Default Ignorable Code Point (DI)	✘
Dash (Dash)	✘
Deprecated (Dep)	✘
Diacritic (Dia)	✘
Emoji Modifier Base (EBase)	✘
Emoji Component (EComp)	✘
Emoji Modifier (EMod)	✘
Emoji Presentation (EPres)	✘
Emoji (Emoji)	✘
Extender (Ext)	✘
Extended Pictographic (ExtPict)	✔
FC NFKC Closure (FC_NFKC)	Caution Sign
Grapheme Cluster Break (GCB)	Any
Grapheme Base (Gr_Base)	✔
Grapheme Extend (Gr_Ext)	✘
Grapheme Link (Gr_Link)	✘
Hex Digit (Hex)	✘
Hyphen (Hyphen)	✘
ID Continue (IDC)	✘
ID Start (IDS)	✘
IDS Binary Operator (IDSB)	✘
IDS Trinary Operator and (IDST)	✘
IDSU (IDSU)	0
ID_Compat_Math_Continue (ID_Compat_Math_Continue)	0
ID_Compat_Math_Start (ID_Compat_Math_Start)	0
Ideographic (Ideo)	✘
InCB (InCB)	None
Indic Mantra Category (InMC)	—
Indic Positional Category (InPC)	NA
Indic Syllabic Category (InSC)	Other
Jamo Short Name (JSN)	—
Join Control (Join_C)	✘
Logical Order Exception (LOE)	✘
Modifier Combining Mark (MCM)	✘
Math (Math)	✘
Noncharacter Code Point (NChar)	✘
NFC Quick Check (NFC_QC)	Yes
NFD Quick Check (NFD_QC)	Yes
NFKC Casefold (NFKC_CF)	Caution Sign
NFKC Quick Check (NFKC_QC)	Yes
NFKC_SCF (NFKC_SCF)	Caution Sign
NFKD Quick Check (NFKD_QC)	Yes
Other Alphabetic (OAlpha)	✘
Other Default Ignorable Code Point (ODI)	✘
Other Grapheme Extend (OGr_Ext)	✘
Other ID Continue (OIDC)	✘
Other ID Start (OIDS)	✘
Other Lowercase (OLower)	✘
Other Math (OMath)	✘
Other Uppercase (OUpper)	✘
Prepended Concatenation Mark (PCM)	✘
Pattern Syntax (Pat_Syn)	✔
Pattern White Space (Pat_WS)	✘
Quotation Mark (QMark)	✘
Regional Indicator (RI)	✘
Radical (Radical)	✘
Sentence Break (SB)	Other
Soft Dotted (SD)	✘
Sentence Terminal (STerm)	✘
Terminal Punctuation (Term)	✘
Unified Ideograph (UIdeo)	✘
Variation Selector (VS)	✘
Word Break (WB)	Other
White Space (WSpace)	✘
XID Continue (XIDC)	✘
XID Start (XIDS)	✘
Expands On NFC (XO_NFC)	✘
Expands On NFD (XO_NFD)	✘
Expands On NFKC (XO_NFKC)	✘
Expands On NFKD (XO_NFKD)	✘
Bidi Paired Bracket (bpb)	Caution Sign
Bidi Paired Bracket Type (bpt)	None
East Asian Width (ea)	neutral
Hangul Syllable Type (hst)	Not Applicable
ISO 10646 Comment (isc)	—
Joining Group (jg)	No_Joining_Group
Joining Type (jt)	Non Joining
Line Break (lb)	Alphabetic
Numeric Type (nt)	none
Numeric Value (nv)	not a number
Simple Case Folding (scf)	Caution Sign
Script Extension (scx)
Vertical Orientation (vo)	U