U+2621 CAUTION SIGN
U+2621 was added to Unicode in version 1.1 (1993). It belongs to the block 
This character is a Other Symbol and is commonly used, that is, in no specific script.
The glyph is not a composition. It has a Neutral East Asian Width. In bidirectional context it acts as Other Neutral and is not mirrored. In text U+2621 behaves as Alphabetic regarding line breaks. It has type Other for sentence and Other for word breaks. The Grapheme Cluster Break is Any.
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.
Others have used variations of the symbol in their textbooks, and computer scientist Donald Knuth introduced an American-style road-sign depiction in his Metafont and TeX systems, with a pair of adjacent signs indicating doubly dangerous passages.
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-Escape | ☡ |
| Wrong windows-1252 Mojibake | â¡ |
Elsewhere
Complete Record
| Property | Value |
|---|---|
| Age (age) | 1.1 |
| Unicode Name (na) | CAUTION SIGN |
| Unicode 1 Name (na1) | — |
| Block (blk) | Misc_Symbols |
| 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) |
 |
| Lowercase (Lower) | ✘ |
| Simple Lowercase Mapping (slc) |
|
| Lowercase Mapping (lc) |
|
| Uppercase (Upper) | ✘ |
| Simple Uppercase Mapping (suc) |
|
| Uppercase Mapping (uc) |
|
| Simple Titlecase Mapping (stc) |
|
| Titlecase Mapping (tc) |
|
| Case Folding (cf) |
|
| ASCII Hex Digit (AHex) | ✘ |
| Alphabetic (Alpha) | ✘ |
| Bidi Control (Bidi_C) | ✘ |
| Bidi Mirrored (Bidi_M) | ✘ |
| Bidi Paired Bracket (bpb) |
|
| Bidi Paired Bracket Type (bpt) | None |
| Cased (Cased) | ✘ |
| Composition Exclusion (CE) | ✘ |
| Case Ignorable (CI) | ✘ |
| Full Composition Exclusion (Comp_Ex) | ✘ |
| 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) | ✘ |
| Dash (Dash) | ✘ |
| Deprecated (Dep) | ✘ |
| Default Ignorable Code Point (DI) | ✘ |
| Diacritic (Dia) | ✘ |
| East Asian Width (ea) | Neutral |
| Extender (Ext) | ✘ |
| FC NFKC Closure (FC_NFKC) |
|
| Grapheme Cluster Break (GCB) | Any |
| Grapheme Base (Gr_Base) | ✔ |
| Grapheme Extend (Gr_Ext) | ✘ |
| Grapheme Link (Gr_Link) | ✘ |
| Hex Digit (Hex) | ✘ |
| Hangul Syllable Type (hst) | Not Applicable |
| Hyphen (Hyphen) | ✘ |
| ID Continue (IDC) | ✘ |
| Ideographic (Ideo) | ✘ |
| ID Start (IDS) | ✘ |
| IDS Binary Operator (IDSB) | ✘ |
| IDS Trinary Operator and (IDST) | ✘ |
| InMC (InMC) | — |
| Indic Positional Category (InPC) | NA |
| Indic Syllabic Category (InSC) | Other |
| ISO 10646 Comment (isc) | — |
| Joining Group (jg) | No_Joining_Group |
| Join Control (Join_C) | ✘ |
| Jamo Short Name (JSN) | — |
| Joining Type (jt) | Non Joining |
| Line Break (lb) | Alphabetic |
| Logical Order Exception (LOE) | ✘ |
| Math (Math) | ✘ |
| Noncharacter Code Point (NChar) | ✘ |
| NFC Quick Check (NFC_QC) | Yes |
| NFD Quick Check (NFD_QC) | Yes |
| NFKC Casefold (NFKC_CF) |
|
| NFKC Quick Check (NFKC_QC) | Yes |
| NFKD Quick Check (NFKD_QC) | Yes |
| Numeric Type (nt) | None |
| Numeric Value (nv) | NaN |
| 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) | ✘ |
| Pattern Syntax (Pat_Syn) | ✔ |
| Pattern White Space (Pat_WS) | ✘ |
| Quotation Mark (QMark) | ✘ |
| Radical (Radical) | ✘ |
| Sentence Break (SB) | Other |
| Simple Case Folding (scf) |
|
| Script Extension (scx) | Common |
| Soft Dotted (SD) | ✘ |
| STerm (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) | ✘ |